I don't think it's all that obvious that he'll continue to improve. He's getting lots of goals right now but I'm not seeing creativity in his game. For him to improve further, he'd either have to score more goals than he is currently or add a creative side to his game. I guess he could score a few more, not sure how many more though. A lot of his strikes this season have been belters, it's hard to keep that up.
As for being a major loss for the premier league, what does that statement mean? If it's for me personally, then I wouldn't care. He's not a great player to watch for me. If it's for the league as a whole, again, he's not like an Henry or Ronaldo who dominated the league or an RVP (IMO) over the last two and a bit years who did the same (to a lesser extent). He's more at the level of a Mata who is just falls a bit below that level, and like I said, he isn't great to watch IMO, which reduces how big a blow he'd be.