Hi mostar, welcome to the forum!
It's my understanding that the core devs are running one or more delegates that have naturally been voted in as 100% paid positions. Some of those are being run on behalf of a core dev. In the future it is possible that a single delegate might fund a hundred developers/entire software house, clearly we're not there yet.
With the market cap & price where it is, if a developer is unable to continue to fund their efforts via BTS, we'll need to find alternative funding, perhaps from a VC who can see the potential of Bitshares. Naturally, the core devs are extremely important to Bitshares continued success.....however, given what has been built already, I believe that the platform will continue to grow regardless of any hurdles, it just may take longer.
I expect that to date, the devs have been funded via a combination of startup capital, self-funding & BTS selling.
Others who are better informed may well jump in here if I have any of this wrong! All the best.....