At first when I read it did leave, I was really upset... but after I watched it... well, I'll just copy-past my post from Bulbagarden:
Wow, I totally loved this episode so much that I can half-forgive them for that. I'm so in love with this show that it's really crazy! I cried... my Ambi...
After watching this episode, if to ignore the fact we had no build up except previous episode... (and how there was no reason to do that) they actually did great this episode!
There sure was emotion there! From the moment Dawn was freaked that Ambi disappeared it was obvious Dawn began to understand it actually wants to do ping pong... and then when the twerps find Ambi they find it playing ping pong (against the wall XD) and Dawn tell the group Ou wants Ambi on his PPP training center...
Dawn ask Ash what he'd do... Ash has a flashback of Aipom stealing his hat during the Kanto GF (we see Max there), catching Aipom, Aipom evolving (which Ash didn't even see so it's ridiculous he has a flashback to that), and Ambipom in Contest with Dawn
Earlier in this episode Jessie has a flashback to her using Aipom in the unofficial Contest (I think she blames Meowth for the lose and says if Aipom stayed with her she could win)
Ash and Brock tell her the trainer has to put the Pokémon's feelings above all (or something like that)
Dawn agree but it's so obvious she wants to cry now but force herself not to
The next day Ou is about to leave but Dawn stop him and ask Ambi what it'd like to do
Dawn hand Ambipom a Pokéball in a Ball Capsule (which symbolise Contests) and a ping pong ball - and she tell Ambipom to choose what it'd like to do
At first, Ambi takes the PP ball but immediately after that the Pokéball too... and then Ash and Dawn's hats... and it begins to play with these things
At first I thought Ambi tried to say it loves all these 4 things (Contest/PPP/Ash/Dawn) but it wasn't the case... Ambi returned Ash and Dawn their hats, became serious and thought about it... then it looked like it decided so Dawn handed her hand to it and Ambipom returned her the Pokéball but kept the PP ball - which means Ambi chose PPP over Contests
Ou tell the twerps his training center is in Vermilion City and that they can visit whenever they want (something like that)
Since Ambi clearly chose PPP over Contests, I doubt we'll ever see it again since Dawn probably won't want to take it even temporarely from PPP to do Contests which it don't love as much as it used to... but since they actually bothered to tell us where Ambi is exactly in - who knows... Ambi might watch Dawn in the GF on TV (like Squirtle in Johto League) and Ou will contact Dawn and send her Ambi... (we can assume Dawn gave Ou Ambi's Pokéball, the Pokéball in Ball Capsule wasn't necessarily Ambi's, it was just used as a symbol of Contests)
So actually, that was a great episode in my opinion and while I wouldn't expect that I hope and think we might see Ambi again... since after all they bothered to let us know where it is now
And it sure cares about Ash and Dawn (and I think it still loves Contests, even if less than before... it did have to think for a moment until it chose PPP over Contests)
I really like these random competitions like this PPP and Pokéringer... all these things should be recurring and not once in a few years...
I'll miss Ambi... at least they did this episode as good as possible... I think
Oh and Jun isn't with the twerps at the end so I guess we're supposed to assume he left after the PPP competition ended
Pokémon PingPong Competition! Ambipom Perseveres!!
