I'd be tempted to take a long, hard look at Britt simply because he proved he can be a productive receiver with poor QB play. If Goff improves under McVay then Britt will benefit from that.
The other factor that comes into play is that the OL is so poor that a lot of capital needs to be invested there in terms of both free agency and the draft in my view. Bearing that in mind, can we afford to weaken other areas of the offence by not resigning Britt? Obviously depends on the contract as well.
This point could just as easily be made about Tru Johnson as well. That CB group is very poor without him and resources are more urgently needed elsewhere. If Johnson leaves then we'll have lost most of our secondary that Fisher brought in and developed (and he did develop them, it was about the only thing Fisher was consistently good at). TJ is a free agent as well so if he was to leave that would be all of them gone (the McSafeties, Tru and JJ). Good teams don't draft/develop players only for them to leave at the first opportunity.
Sorry, went off on a bit of a tangent there