It's still possible to port-out your Google Voice number for a fee. I wouldn't rely on keeping Google Voice after Google kills the legacy accounts. If you have to, port out to a different SMS service (you could port back in to consumer Gmail if you really wanted to).
Back when legacy accounts weren't legacy, Google Voice was free for G Suite (I think they are now called "unmanaged") and Google is trying to get rid of those accounts in favor of newer paid "managed" accounts.
You can transfer a phone number from that sort of account to a Gmail account. I just tried it and it seems to work. Go into settings then transfer. It takes you to the legacy page to do the transfer, oddly.
> A Voice for Google Workspace account number to any other type of Google Account, including personal accounts and accounts using a different Google Workspace domain.
I am confused if my Legacy G Suite account is considered a Google Workspace account of if it's something different.
Back when legacy accounts weren't legacy, Google Voice was free for G Suite (I think they are now called "unmanaged") and Google is trying to get rid of those accounts in favor of newer paid "managed" accounts.