I don't think any reasonable person thinks they should dump Brady today and give the keys to JFG after one game. What this does, though, is give a possible glimpse into the future and the concept that the Pats days post Brady won't be dark and continued excellence is possible.
I think they need to try and keep Jimmy, but it will be tough. Realistically, Josh leaves at the end of the year and whichever team he ends up will trade for Jimmy next summer or before the draft and the Pats grab draft bounty.