If he’s found to have broken the rules, it’s possible he’d be suspended from parliament and subject to a recall election. However, he has resigned from this position himself instead, which means there will be a by-election for that seat.
It’s widely perceived that he has done this to distract from the investigation, with the view being that if he runs, then wins, a parliamentary suspension looks like a coordinated attack on someone who has just proven he has local support.
The major UK parties have decided not to field candidates in this election, claiming it is a distraction tactic and a waste of resources. This will leave Farage campaigning head-to-head with a man dressed as a bin, neutering any claims that this is a “real” election win (as well as generating plenty of entertaining news footage over the next few weeks).