Simms was injured. Jeff Hostetler started for the Giants in the '90 postseason.
Even worse! And surely Seifert would have come up with a way to beat the Bills in the game.
Seifert has proven to be one of the most overrated coaches ever, IMO, riding Bill Walsh's players and playbook for most of his SF tenure
I suspect that Seifert would have tried to outgun Buffalo, which, as previous games had shown (see earlier playoff game vs. Miami) was not a smart idea. Parcells idea of ball control against them was, in essence, genius.