Hadn’t Nixon already resigned at that point?
Will Hillery give up her White Hut run? Doubtful
Yes, although the deal with Ford to get the pardon may have already been made.
The point is that there is a precedent for pardoning people without specifying the crimes and without a conviction.
As a mechanism for concealing wrong-doing in government, I would be pretty confident that our Founders would have opposed doing this, although they might have recognized that an out-of-control prosecutor can make life hell just by prosecuting.