At the end of the day if you invest in a Yahoo premium email, and Yahoo announces after 10 years they will merge with AOL and AOL discontinues email because they introduce a social service ..
That's ten years of your life via electronic mail that's gone from future usage.
You can't control what any company does.
Because, at the end of the day, you're a customer of a company that has a product. You pay for it. You have a license to usage of that instance of the product.
If they get divorced, get hit by two law suits, or die a horrible death by muppet murder with a lethal rerun, .. you haven't paid for the future, as much as you emotionally might think so. You paid for that instance of the product with 12 months of support and download access to whatever new version comes out. Not a future license or future development. They can't tell what the future brings, neither can you.
You're free to buy a license, or how many you desire. You're free to donate any significant amount via donation or investment into the company (pending their acceptance), or not. You're free to cover their legal fees or create a fund in their name in case of divorce or buy-out-in-future-by-shared-partner(s).
Or you can just buy a license so you can run a forum, because you buy forum software because you believe you need it.
500,000 people holding off waiting to see if a company will make it.
Results in 500,000 x less money invested in a happy wife with a credit card, a happy shared-partner being able to pay the bills, a happy attorney getting paid to win law suits, or whatever you might worry about.
If people think this is a good product, and they think it is worth at least $140 right now. And they need a forum product. .... Just buy it.
Or think of it this way.
You want a good web site with great content, visited a lot of times by happy users.
You hold of and don't have that.
Or you get a license now and for those years this company was around you at least had a good web site with great content, visited a lot of times by happy people.
And, when in doubt: Don't do it.
tl;dr
If you don't want to pay for forum software, don't trust the guys that run this company, or don't believe in a future for the company, or have any doubts: Don't invest in a license. You will lose by not having the site you perhaps wanted.
If you do want to pay for forum software, and want to see them succeed in the long run. Invest in a license. It helps them, but more importantly: You have the site you perhaps want.