The question for me is sponsoring more about promoting the brand or selling t-shirts? Take a company like "Bad Boy" for example. When they sponsor Chris Weidman do they sell a ton of Chris Weidman walk out shirts or is whats beneficial the fact that Weidman is affiliated with Bad Boy and their brand is all over his shirts and shorts and promoting the brand.
If its the former, those companies will never get that money anymore and will drop their UFC fighters. If its the latter and the UFC allows fighters to use 1 or 2 sponsors of their own, I could see many sponsors choosing to stay.
On another note, its rumored that Reebok is spending a million a month on sponsorships and it will be split among the fighters that fight during that month. On average, there are four cards a month and at least 11 fights (22 fighters) on each card. Thats $11,363 per fighter. Which isnt bad until you realize that fighters are paid on tiers depending on where they are ranked. So lower ranked fighters will likely see less than that.
One other point that I saw on twitter is the UFC may have screwed themselves when it comes to matching contracts with Bellator. For example, if Bellator includes a clause in a FA UFC fighter's contract that says "Fighter may personally select his sponsors and place sponsors logos on gear", the UFC wont be able to match that under the current uniform policy. Unless it wants to give select fighters the option of not following the policy.