Specifics can go all over the board in different cases but the above example typifies what tends to happen with founder interests in a typical Series A funding. Founders can resist but, if they want the money, they often have to agree to just such terms.
I have seen all sorts of cases where such scenarios lead to bad outcomes for the founders. I have seen many others where things work out great for all concerned. It is just one of the risks of taking in VC funding but it is a very real one for the founders.
Even where a founder has largely vested his interest, or where his termination triggers enough accelerated vesting that he largely vests, he will find himself vulnerable in any down-round scenario. In that case, I have seen VCs (in the most abusive types of cases) do as much as a 100 to 1 "reverse split," reducing everyone in the company to 1/100th of the interest that person held before a new funding, and then inject new funding (at a much-lowered company valuation from that used in the most previous round) that leaves the VCs with substantially all the ownership in the company (they being the only ones with the funds to participate in the highly dilutive round) apart from the employees they wish to keep and such persons will then have their options "refreshed" to give them modest equity pieces as incentives to keep going forward. While the 100-to-1 cram-down is absurdly extreme, many cases will arise of more modest ratios used by VCs that have the effect of sharply reducing the early-stage equity interests in a company and that clear the way for new grants to be made to continuing founders who, because of such grants, will keep something close to their original percentage in the company while a terminated founder gets sharply reduced.
Hate to sound boring with logistical details but these two illustrations are among the most common techniques used.