Yes, but on cartridge this occurs a lot more rarely than on Virtual Console where freezes seem to be more common. Though the rate of your save file deleting itself varies based on the situation/glitch/(and stressing: the save battery on your cartridge could die/not read the save), I've unfortunately lost many saves while handling long name glitch item names, or getting a freeze from arbitrary code execution or walking out of bounds. If you have a means of unofficially backing up your save file, I recommend it. If you're not a fan of emulation/custom firmwares, the Mega Memory Card Game Pak is good for that (but in its original retail release it can't connect to a computer to import/export saves). Another action that erases the save file all the time is saving if your name is over 10 characters long.

Most glitches which don't freeze the game will leave your save file intact however ^^ (except the Hall of Fame entries, in which case you may want to avoid handling glitch Pokémon)

A: I don't know the full answer because a few have tried all workarounds and still not found success, others have found success after trying one or more of the following:

*Changing pockets before using the Coin Case (important even though it sounds like a minor change)

*Sticking with Bellsprout/Machop as the previous cry

*Doing the exact movement patterns in the video

*Catching new 'slide Pokémon' for the correct slot many times until one works (or using one of Crystal_'s specifically made ones https://youtu.be/PsIb3OZaYAs?t=247

*Double checking the bootstrap party (with the Quagsire, its held item and move 1, etc.)

*Making sure your box names are exactly right. Even the omission of an apostrophe from the characters, mixing up the letter "x" and the multiplication sign, etc. can break the code.

*Making sure you're not doing the glitch on Stadium 2/or an outdated emulator such as early versions of VBA (likewise you need to make sure you're not using one of these for dokokashira door glitch). This is because of bad Echo RAM emulation on those emulators. Coin Case glitch and Echo RAM ACE works on: A real Game Boy family system, Nintendo 3DS Virtual Console, Nintendo GameCube's Game Boy Player (iirc, not 100% sure)

*If the menus are extremely slow/glitch out, the game might actually not be frozen; you just have to spam B. You may be able to work around this by turning off the "menu account" setting in the options (it's an actual official option in-game like battle animations, though obscure); which is responsible for printing the characters on the Start menu. Coin Case glitch is known for glitching out how the characters are printed/print speed. Also exiting the Coin Case display with B and not A might work.

A: First it sounds simple but make sure you do the scrolling up for a long enough time (but unless stated in the glitch's instructions it's usually only up to about 5 seconds max). If you only get Bad Eggs and never get a regular Egg or the second type of corrupted Egg (such as a corrupted species on the Egg), DMA may be responsible. You may have heard of cheat codes called Anti-DMA. Basically, there are locations in the memory which determine the variables like your Pokémon's data while playing. In Emerald (a lot more so than Ruby), these are randomised including in your PC box. Hence, whether the glitch works or not is luck based.

Originally when this glitch was found, the strategy was to use clones of Seasor/Dots in succession but this was actually found to give a low chance of success. In fact (from how I gathered from Metarkrai; an expert on this), you may be better off using an empty space. The solution to this is something called a "corruption initiator", which increases the chances of success, even though it is still not 100%. A relatively easy one to obtain is a modified version of Pluses the in-game trade Plusle.

For more information on "corruption initiators"; which make Pomeg glitch success more likely: https://glitchcity.wiki/Corruption_initiator

For arbitrary code execution it's a bit different, because a method that can  'nop slide' (e.g. glitch move animation ACE) can effectively remove all luck based elements. Also in the more poorly documented Ruby ACE, lots more addresses are not subject to DMA; so once the ACE is set up you can (as far as I know) do ACE without any luck elements too; but Ruby ACE currently requires an in-game trade (and Metarkrai thinks it may be tedious to set up). Ruby EN (v1.0?) ACE is good for accessing the sound test which doesn't exist in English Emerald (but exists in Japanese Emerald iirc).

A: The glitch occurs when no 0x50 byte is found in the (first 20?) characters of its name. However, the name of the move depends on the state of the RAM; including how many 0x50s bytes exist in it and so on. This can make the glitch unpredictable.

In short, the glitch depends on chance. If it stops working changing the nickname lengths of Pokémon you have/the number of x80 quantities or Ethers you have etc. was thought to work; but this doesn't guarantee success, is hard to verify and won't necessarily even work. The best option in that case unfortunately is to clear the save file with Up+Select+B and start again in the hope that next time when you flash the name/do the scrolling it will work or eventually work. In fact (though I'm not very knowledgeable about speedrunning), I'm under the impression speedrunners stopped using the glitch because of its luck-based nature and how recurring failures could heavily impact the run.