It also seems kind of spiteful? Revivify seems like an odd thing to counterspell, much better to stop a big damage spell or heal. Revivify only revives with 1 hp, so a strong breeze would put the barbarian back down. The party would have to commit multiple actions to healing him up while he runs for his life.
Instead, one of the players basically has to sit out for the finale of the campaign. Assuming the party succeeds, he can’t conclude the story with everyone else and the player just zones out during the epilogue.
I think a good twist mechanic is one you can react and adapt to. If the dragon countered a random damage spell, the players are introduced to the twist in a less consequential way and can now adjust their strategy to the new information. Here, they are punished for something they didn’t even know could happen (unless they have meta knowledge from other campaigns, which you should never assume) and can’t do anything except shrug and accept that their friend is dead.
Look into used Bolts, they’re a steal right now. I got a 2020 Premier with 20k miles and a new battery for 14k after rebate.