Why not? Michael cannot exist without Mikkel and vice versa.
The beginning of the show said Time is linear or something like that. Everything repeats over and over. So if Mikkel didn't exist in 2019, he wouldn't have traveled to 1986,and thus Mikkel might not exist at all. It's hard to explain, but don't be lead by the old sci-fi notion that the universe or time or whatever would crumble if two of the same persons meet. For Time itself, both Mikkels/Michaels would be just two living bodies and nothing else. Damn, I could write for hours about this and still explain nothing lmao