Are you referring to custodial wallets where you create an account on some website, and the company behind it holds Bitcoin for you? If yes, then it is important to remind that in such case you have no physical control over the coins, which means you kind of already lost them once handed over to random guys on the Internet! What you have is a promise to return coins on demand, but as with other similar promises it can well be broken for whatever reason, which usually results in you getting failed expectations regarding safety or possible income. If a company closes down, goes bankrupt, or turns out to be a malicious scheme created to play games with naive newcomers, you lose your coins for good as if you never possessed space inside the blockchain. As I said, the only time you can claim that coins are yours is when you have a corresponding private key to an address with those coins. On the other hand, if a wallet is non-custodial, hosted on a public repository on GitHub, and follows all cryptocurrency wallet specifications such as BIP39, you can be sure that if it stops functioning, you can take your private key or seed phrase and import it in some other wallet supporting the same standards. In this case, no matter what happens to people developing the wallet, you can always transfer to any place you like: you keep controlling your funds while choosing services to manage interactions with the blockchain.