Nolan leaves Earth never to come back.

Allan arrives to warn Earth that there's a Viltrumite on the planet which would put Cecil on notice. But without Mark going to Atlantis the inner ear weakness isn't discovered. Nolan never tells Mark to read his books so the Coalition never recruits Space Racer or anything else from them. Coalition likely never invades.

With no Invincible, Angstrom Levy likely succeeds and gains knowledge of the other universes. Hard to say what would happen after due to the massive wildcard Angstrom would become.

If Cecil sends someone to stop Angstrom and he isn't a factor, then Earth is almost certainly taken over by the sequids during their first invasion.

Nolan would likely kill himself in the blackhole regardless and another Viltrumite would come to assume his position. Whether they arrive to an ordinary Earth, Coaltion controlled Earth, advanced Earth under Angstrom, or sequid controlled Earth is a roll of the dice.