No, FiOS TV isn't going away anytime in the foreseeable future. But Verizon's comments earlier this week make it clear that they don't see much future in traditional linear pay TV (i.e. "cable TV"), so you definitely should NOT expect them to dump more money and time into improving FiOS TV.
Those new boxes that would "stream" FiOS TV that you're referring to, that was going to be a new Verizon managed IPTV service (the same kind of TV transmission technology as used by AT&T Uverse TV and Google Fiber TV, both of which are getting phased out). It was developed out of the OnCue technology that Verizon acquired years ago from Intel. This new service was beta tested last year. For whatever reasons, Verizon shut down the beta test months ago and decided to completely kill that project. I think they realized that managed IPTV's moment is quickly passing, and the future of video is OTT (which can be accessed over the open internet, via any provider's connection, while managed IPTV can only be deployed over a provider's own network connections).
It will be interesting to see what happens with Dish and all of that spectrum they have. I don't think that Sling TV fits the bill for what Verizon wants and needs in an OTT TV partner, although if they ended up acquiring all of Dish (not just their spectrum), then I guess they'd get Sling TV too. But of course, an acquisition like that would take a long time to put in place. And Verizon needs an OTT TV partner PRONTO because they have to have something set up and in place by 4Q18 when they launch 5G home broadband service.
I still think that Sony's PS Vue service makes the most sense as a partner for Verizon. Sony noted in a presentation this week that the "market and future business model" for PS Vue "remains uncertain". Which is understandable since, after 3 years in business, they reportedly still don't yet have 1 million subscribers (despite the fact that they seem to get good all-around reviews from users, and the service seems to have few flaws, other than having fewer locals on board nationwide than other vMVPDs and also lacking Viacom cable channels). But fear of becoming an also-ran behind the three big boys (AT&T, Google and Hulu) should make Sony all the more willing to partner with Verizon on a co-branded version of the service. And unlike YouTube TV, Hulu and DirecTV Now, PS Vue doesn't yet (AFAIK) have their own targeted digital ad system in place or in development, so they could use Verizon's/Oath's. The partnership could make a lot of sense for both companies. Perhaps Verizon would even want to provide a capital infusion into PS Vue and turn it into a jointly owned venture between Sony and Verizon: call it Vue TV from Verizon + Sony.