They are tearing their team apart anyway. I don't see the point of having a mid-level $55 million AAV QB on a team that has been torn apart. It will make it harder for them to have the money to rebuild and by the time they do rebuild he might not be the QB anyway.
Personally, if I were them I'd look for a young vet free agent or trade for a young vet like Malik Willis or Milton. Then build the team while having more money. But, yes, worst case scenario I'd sign Garoppolo, Flacco, or even Winston before giving Purdy that money for that long.