In theory it'll be yours forever.

The only exception is if your wallet is with a company (e.g., Coinbase, Circle, Xapo, etc.). Any of those company's can go out of business, and if so you'll lose that wallet when they do.

You know that you can have your wallet forever if you have the private key (along with the public key). The private key is proof of ownership.

Now Coinbase and other bitcoin "banks" are fine, they're good, they're convenient. People will say "if you don't own the private key to your wallet, you don't own bitcoin." Technically this is true, you just own an IOU from the bank. BUT, the same applies to every single bank in the world. Your Dollars, Euros, Pounds, etc. aren't literally yours unless they are in your physical possession...like stacks of cash in your home. So, don't let that hype worry you.

Edit: Wait, are you talking about a transaction? Where would you write a transaction and not click "send"?