I tried doing this not long ago in FTB Infinity, and instead of losing itself - it had stuff in it at the time - it caused a client exit, and possibly a crash although I couldn't find one. When I relogged, I found the bag was still in my inventory somewhere.
Therefore, it *may* be possible to stop yourself from losing the Golden Bag of Holding that way.
You might also want to search the Minecraft forums for the utility "NBTEdit" as it can look into your world save data, it's in level.dat and if the Golden Bag of Holding still exists in your world, you might be able to recover it and it's contents. I'm not sure what server admins are capable of, but if you ask politely, perhaps they can look into your save data for your character and retrieve the bag and it's contents for you, if you're playing MP.
Cheers ...
BrickVoid