Was going to post this earlier but barely had cellular
Yes, players are likely to regress TOWARDS career norms, but won't always reach them, especially if they have a lot of PA/IP already banked.
Will illustrate with a simple math example. A fictional player let's say has 4 years of MLB experience and has been a consistent .300 hitter all 4 years. That's his true talent level. The next year after 81 games he is hitting. 400. He's been "seeing the ball well" or had a lot of BAbip luck or whatever. Second half he probably won't keep that up. He'll probably start hitting his usual. 300 and end up with a career year hitting. 350. Or to use the opposite say he has a bad first half. Mechanics not right, getting unlucky whatever and he hits. 200. Well, he will almost certainly regress/progress (don't let me get started on that one LOL) and start hitting closer to his career norms in the second half. But he's VERY unlikely to get back all the way to 300 because he's buried himself so deep. Good chance he hits 300 ish in the second half and ends up with a.250 average and have a career off year.
In neither case if the guy "due" to start hitting like mad or like crap because he was bad or hood before. In the same way if you toss a coin 5 times and get 5 tails you're still no more than 50/50 to get heads next time.