There's also the idea of a snapshot and/or fork. The new vault could be on a brand new blockchain but use the same private keys or have a distribution so all existing balances are present on the new blockchain, so all people would have to do is import their old vault private keys and they have their coins.

Unfortunately, that is how Cryptopia works. I saw a coin upgrade from a non-masternode version with a different PoW algo to a coin that supports masternodes and a newer PoW algo. Cryptopia allowed the old coin to be delisted gracefully, but would not relist the new coin, since it is considered a new coin, unless the listing fee was paid.

The coin dev did not pay the listing fee, and nobody else wanted to, and no one in the community wanted to donate towards listing. The coin is mostly swapped from old to new, and any unswapped old coins, the new coin equivalent would be burned.

The new coin has been doing better than when it was listed on Cryptopia. If Bittrex does charge lower than Cryptopia, perhaps people are willing to get listed on that one instead and contribute accordingly.

If you do a "fork", then you still use the old blockchain, but new vault software, and of course there will be two blockchains after that particular block, the question is if Cryptopia would accept the fork and replace the old coin with the new coin, or have some sort of "in place" swap that instantly happens on the forking block.

This would also render the old vault useless. Just make sure you guys don't inadvertently do a "btc1" and the vault gets stuck.