Would it be impossible for Trump to be charged with a crime even if it can be proven he committed one?

If Trump has reason to believe charges are coming when he leaves office, what's to stop him from resigning the day before inauguration day?

Then, Mike Pence, president for a day, can issue a blanket pardon to Trump for any possible charges related to such and such investigation, just like Ford did for Nixon.

That would take care of the legal quandry of whether a president can pardon himself. Because President Trump didn't pardon President Trump. President Pence pardoned former President Trump.

The president can only pardon federal crimes. The SDNY is investigating state charges.