Yes there have been some wallet companies that have closed already. Just like Multibit: Multibit is Deprecated - Stop using it

If you're planning to keep your coins for a long time @OP, the best way to do it is to use a hardware wallet. It has a price but that price is certainly going to give you a peace of mind.

Although some wallets can be used and also good in keeping your coins as mentioned by some in here like Electrum.