If Dawn ever does come back to the show, how do you think this would affect her relationship with Ash?
To start with, it really isn't entirely clear that she would
come back. I know I've been probably one of the strongest advocates on the other side of this, but still, there's a saying that "A goodbye isn't painful unless you know it's forever". (I think I've brought this up before). Dawn clearly thinks that this is forever...
Wellllll, ignoring my unnecessary side-note... There's four clear possibilities, and I'll do my best to explain which one I think is more likely based on our past examples.
1. It weakens the relationship
Well, we've all seen this story before. When Misty and May both went through their final seasons on the show (Johto and Battle Frontier respectively) their relationship not only went on the back-burner, in one case a rival shipping took over!
Basically, Kenny somehow wins Dawn over in Ash's absence, overriding the entire vibe of the series (ignoring DP 180's dub, lol).
Again, entirely possible. Of the three girls we've had in the dub (and hence at the point where I can really analyze them) Dawn is the least "romance-oriented". May and Misty always emphasized the romantic nature of things or the need for romance or whatever, but Dawn's been rather mum on the topic. When Lyra seemed to go the same way, it freaked her out a bit.
To extend the point a bit further, many of the furthest lengths we've seen Dawn go to to impress Ash have never been explicitly for winning him over. Even when she dresses Piplup up to cheer in her place, she seems more motivated in showing Ash how dressed up (and supportive) Piplup is (and hence that she is).
I actually think this is one is the least likely to happen to Pearlshipping should Dawn return. Given that she'd be the only character to take a break before coming back, her return would likely be at worst neutral.
Speaking of which...
2. Was... was something supposed to happen?
That is an entirely possible scenario. After all... (cross apply what I said before, but less harshly). Dawn stays where she is right now with Ash, that is to say really close friends.
Again, I think this is highly unlikely. If they're going to go so far as to bring a "shelved" character back, it has to be for a purpose. Either there is some here-to-fore unseen revolt against "The Squeaker" Iris and they have to backpedal, or they make Dawn get further developed as a character. I'm not seeing the former happen... sooo
3. It strengthens the friendship
Basically, Dawn and Ash get closer over the course of their journey (entirely possible, we'd just get more Dawn-cheering-for-Ash scenes).
Again, not likely. If they're going to develop their relationship, and go so far as to bring her back to do it, there's really only one likely outcome...
4. Pearlshipping happens
I would be so happy if this actually happened. I recently rewatched DP191 (and I'm in the process of rewatching the "Paul Final Battle" arc, and it's reminded me a lot of why I like this pairing so much (and why I think I've miscasted them a bit in my current fan-fic, something I hope to fix for the contest).
Dawn goes so far to support Ash, and is so funny in how she chooses to show it. Not to mention, given the extreme high note they left off on, it'd be fun to see it go even farther later on