There are a number of key major players already on board to make this happen on multiple sides of this opportunity, but in the end, there are two major threats to the deal happening:
1/ The first is Melynk. He brings substantial negative PR value to the entire affair, and needs to stay in the background. This really has to be about Ottawa developers and the NCC bringing the Sens downtown, rather than Melynk riding in to save the day by bringing the Sens there based on his own ambitions and ideas. In the end, there is municipal, provincial and federal $'s that can help offset this building, but a lot of this will shrink or disappear if Melynk is the face of the deal. Local business needs to be front and center, and while Melynk can be part of this group, he needs to be in the background, if at all. Optically, the government $'s and rebates can't seem to be just offsetting the cost of a billionaire to get a new stadium - and even worse, a billionaire who doesn't happen to live here. And there is always ample $'s to offset for buildings like this to be built if presented and structured properly. Probably a 1 in 3 chance the deal dies because of Melynk being too involved. Ego has killed bigger deals than this before.
2/ The second risk is deal structure. In the end, the Sens can't really own the stadium. Oh, they can own perhaps a minority stake, and also get a ridiculously sweet heart deal on rent for decades that will essentially amount to getting their cake and eating it too (getting a rink with out having to pay for it), but Melynk has a super deal now in owning the building, parking and all of the infrastructure around Senators revenue. They will quite simply have to give the majority of this up, and focus on making $'s as a hockey team. The deal will still make profitability very achievable with a lot less debt to pay back as well, but philosophically, Melynk might hate giving up control of the building, which could prove a problem. I'd say the Sens group will look at the deal in the end, and realize it still makes sense and can't be done on their own, but perhaps the issue of their stake in the whole deal will be a deal breaker. I'd say 1 chance in 10, give or take.
So I'd guess it's close to 50/50 it happens, and probably better chance it does, than doesn't. But lots that can go sideways. First step is this release to test the fan reaction and get the conversations started.