What a terrible place to be put in as a company: A big opportunity you're incredibly excited about, but contingent on you screwing over the people who have helped get you to where you are in a small way.
I would encourage any founders who are put in this type of scenario to fight back hard. Investors that are worth their while will respect your loyalty and your refusal to go back on your word. If I were a later-stage investor who proposed something like that and the company came back strong saying, "That's not even on the table, because we're not going to do something below the belt" I would gain additional respect for that company.