The main thing about Hartley is, who would replace him? Red Bull and Toro Rosso would want to put a Red Bull Junior in, but there aren't any ready. Dan Ticktum is the most experienced of the lot, with a Macau GP win to his name, but he doesn't have a Superlicence yet.
Honda want a Japanese driver, but Matsu****a and Fukuzumi also don't have a superlicense, while I'm sure Toyota would just love to let Nakajima or Kobayashi join Honda. Their only option there would be Super Formula, but I doubt they'd take anyone from there.
And Wehrlein? As much as he deserves to be in F1, I doubt Mercedes would want him playing around with a Rival engine, AND a Red Bull affiliated team.
Anyone who says Sean Gelael needs their head cleaned out.
Hartley is the best Toro Rosso are going to have for a while, so they may as well work with him to make him into a class Formula 1 driver, we know how good he was in LMP1, he just needs to readjust back to Single-Seater racing.