It seems that once they mark a coin for maintenance, it is gone for good. Never seen a coin going live from maintenance.
Maintenance mode is also turned on if coin code need to be updated to the new release. Personally have very possitive experience with Cryptopia team.
Same here for the most part, however a lot of coins are in maintenance for weeks if not months and are not marked for delisting. 1337 just went into maintenance mode more than a week ago and I had a deposit just when the wallet broke. It shouldn't take weeks to restart/resync a wallet if its facing tx issues or for a mere client update, it's just negligent, everyone loses, clients can't make deposits/withdrawals and cryptopia can't take their well deserved low fees. Quick count shows 19 wallets in maintenance that are not getting delisted, it's quite substantial.