As recently as 2-3 weeks ago when Josh Brolin went back to the IW set, he posted a picture of himself on Instagram in his mocap suit and one of the hashtags on the picture was #ImJustAPurpleGuyLookingForLove. The post was then swiftly deleted within a couple of hours. That's pretty damning proof to me that Thanos will definitely have a love interest in IW. I don't think the assumption that it may be Hela is premature at all, there have been quite a few hints pointing to it including Marvel recently putting Thanos and Hela together in the comics verse when they'd never even interacted with each prior to the Unworthy Thor book. Marvel have a long and proven history of changing things up in the comics to closer reflect the movies.
Also, if Death as a character is going to be IW, I can't help feel that we would have some info about her by now with all this new stuff being released but we've had nothing at all, no word of an actress being cast, no concept art and there's no glimpse of a Death like character in the IW trailer at all. If Death is a completely separate character to Hela then there would be no need for Marvel to hide her whatsoever, however hiding Hela's possible involvement in IW at the moment makes a lot of sense because it's potentially a big spoiler for Ragnarok.
Finally, I know Hela has always been the (Asgardian) Goddess of Death in the comics, but I feel like Marvel Studios are really playing that angle up in a lot of the promo for this film, she's referred to as the Goddess of Death twice in the two minute trailer alone, and it's also emblazened across one of the Hela t-shirts that have been released. It's almost like Marvel are really trying to hammer (pun intended

) the point that she's the Goddess of DEATH (wink wink, nudge nudge) home to the audience.