Marc Rich was pardoned while a fugitive for much more serious crimes.

Assange wasn't pardoned. He agreed to a deal to plead guilty with retroactive detention which meant no additional imprisonment.

A pardon can cover previous crimes with or without conviction.

there is no such constitutional restriction. A pardon can be issued for crimes that are not even known to have occurred or are purely imagined.

Richard Nixon would like a word with you.

You can definitely get pardoned before getting convicted. Trump pardoned Stephen Bannon after he got indicted wire fraud and money laundering, so he never went to trial for that.

https://www.forbes.com/sites/alisondurkee/2021/05/25/steve-b...

He is getting a conviction. This is a plea deal. He will be admitting to the crime of conspiracy after which he will be a convicted by the court. He will then be a convicted felon and could be pardoned, but I doubt that is really an option. (Not 100% on the felony thing, I haven't seen how this is being charged.)