"Yes, but..."

If Trump pardons Roger Stone, then Stone can immediately be hauled before Congress or a grand jury to testify about his crimes and 2016 conspiracy without the protection of the fifth amendment. If he lies, he can be indicted again. https://t.co/Bz8xw7SREf

— Buckle Up (@Buckleup36) February 13, 2020

The question of a pardon and the 5th Amendment is a "yes, but..." question, the kind of answer lawyers love to give, and non-lawyers hate to hear.

Eugene Volokh, at the link, does a decent job of laying out the parameters, but skips lightly over the question of the reach of the pardon.  For one thing, Roger Stone has already been convicted of three crimes on 7 counts (if I read the news accounts correctly; they aren't really precise about what charges he was convicted of, or what counts apply to which charges).  He can be forced to testify on those matters, because he can't be further convicted on them (double jeopardy; which is also the 5th Amendment).  The main reason you don't do that is that he's a convicted felon, how reliable is his testimony now?  Although that's what Michael Cohen is, and his testimony was avidly sought.

If Stone is pardoned, then yes, he can be compelled to give truthful testimony, but only as to the matters covered by the pardon.  If the matters are arguably outside the reach of the pardon (and only involve federal, not state, crimes; that's an important distinction.  SDNY passed off an investigation arising from the Mueller report to New York state, who is investigating Trump under state law.  Nothing he nor DOJ can do about that, except claim a sitting POTUS can't be hauled into state criminal court.  That would test the memorandum that is accepted as law by the DOJ just now, so that would make an interesting court case.), then the 5th Amendment protection is preserved.  That is, admittedly, a thin sliver for Roger Stone (or anyone) to hide behind; but it might make grounds for an appeal of a trial court ruling on contempt for refusal to testify.

OTOH, Stone is apparently out of money and relying on the kindness of strangers to raise money for his appeal now.  Frankly, he's in a world of hurt with or without a Presidential pardon, and however that comes down, there may well be investigations into Trump that don't stop just because he's a former President.  A Democratic President might not want his AG to pursue Trump (another argument for making DOJ independent of politics, frankly), but that won't stop states from pursuing criminal investigations.  That kind of thing Trump can only escape by pulling a Roman Polanski; unless he tries to pardon himself on the way out the door, or tries to resign in order to get Pence to do it.

Which would be a whole new round of "Constitutional Crises."  Let's not get that far out on that limb, yet.*

*besides, it wouldn't affect the state investigations and possible criminal charges, so what good would it really do him?