Preparing to wait at least 12 months after release to bother playing this... Assuming it isn't abandoned at launch.
I'd assume they'll cut the team down to the core after launch.
Depending on the sales they might have to cut a little more.
There isn't really anything comparable in the indie market, so it's hard to say how successful it will be, with or without being a proper UU sequel.
Sometimes even bigger AAA titles like Assassins Creed have weak sales numbers, depending on how well they catch on with the general public.
I remember one had around 20k, which is basically nothing for an IP like that.
It will largely depend on first reactions towards it.
Considering that it's a KS game and many of the funders might be displeased, it will probably start out at a PR negative. So that's bad.
Their chance - and I guess that is the reason why the game is the way it is - lies with streamers and influencers. You've got a lot of physics based nonsense you can show around and which might be fun to watch (if the players get it, which is another minefield of negative criticism). That, coupled with the generally non-aggressive art style, could get in some sales.
If I had to guess - and that's my guts speaking again - I'd say it will sell 20-35k units at 30$ in the first three months, accumulating to 90-100 over the next 1.5 to 2 years.
That is, if it runs okay-ish.
Is that enough? Well...
Steam takes a good 30% cut on your profits and the state takes quite a bite out of the rest. I don't know the tax law in Massachusetts. There are states that have 6% tax rates on profits, there are the ones that have 25 and then there are the robber knights and commie states that take 50% (looking at you France).
If you wanna calculate cautiously, count 30% of the remaining profits for taxes. That also includes social security if your state has laws in that regard.
So with what you earn on steam, cut that by 30% and you'll have the "real" profit.
With that cash Otherside now has to pay its employees and publisher. I believe at another point I mentioned that over the 1.5 years of financing, Otherside probably got 1.5 million from 505.
Considering all of that Underworld Ascendant should break even at around 100k units.
Which is technically possible. Legend of Grimrock had 600k sales at I believe 15$ over the course of a year. Almost Human was roughly the same team size I believe.
The thing is, LoG had way more traction, by basically re-introducing a classic genre with quite some success. Their big advantage was - and you probably already guessed it - a scene of big name influencers. Notch among others recommended the game.
I don't really see the same happening for UA. At least not at the moment.
On it's own it can still make those 100k. But it's gonna be tough and a long road and there must not be any glaring issues that shy away players.
Core gameplay has to be at least okay. Combat has to be okay. Magic has to be okay. There must be very clear hooks why these core systems are nice and interesting. You can pack that in a trailer and people will probably like it.
But yeah...
I'll be dead honest: I personally hope they have success with this, even if its not really Ultima Underworld, but if I was an investor, I'd start sweating now.
505 might have their money back by 2020. The game will have entered steam sales by then. So that is where the "real" profit starts, which is of course way lower than it would be at launch. But that's just how it is. UA's chance there is to become one of those games, that are in every sale and everybody has it, even though people never play it. It may sound derogatory but it might be successful with a "Bad Rats" sales strategy.