Quite frankly, I want to give the father a chance.
You got to remember, MC is a sage living a second life.
I trust that MC had the ability to character check the father before serving so faithfully.
Why give him a second chance? When he himself didn't give the MC a first chance to defend himself from his "dear son's" allegations?
He could have the MC's room searched for the money or other suspiciously pricey items that he should not have been able to buy on his butler's stipend or ask around to ascertain his spending habits, or even IF there was money missing from the house's coffers. He did no such thing.
He could have send a team to investigate IF there are monster corpses in the surrounding area or even have the MC prove that he can kill powerful monsters, he chose not to.
Heck he could just have the fang that the MC showed him checked by an expert to ascertain its authenticity. But again he chose to deem it a fake out of hand and then declare the MC worse than trash and subsequently banish him from the only house he's ever known, even after years of faithful service with nothing but the shirt on his back and in a most insulting manner at that...again on unconfirmed allegations from ONE person.
He deserves no pity, nor a second chance. I sincerely hope the MC won't give him a second chance....but we all know that 99.9999% of MC's in Japanese media are goodie two shoes because "the MC must be selfless and forgiving always" for ...reasons...
I just hope that when he'll inevitably chose to help the feudal lord, he'll charge him an arm and a leg so he can fund his spell research...at least that is what I would expect someone whose supposed to be a sage and has the wisdom of having lived already once to have.