My last job did this. They offered more for those who had worked there longer. People with over 15 years got about a years pay and they all took it. People who had been there under a year got nothing so they all stayed.

I was going to take then they withdrew the offer for all devs. I think a lot tried to take it and they realised no one would be left. I would have got 3-4 months pay. Loads of institutional knowledge lost though, i left anyway a few months later.