You should have no problem exceeding 200K with your Bonnevile. I say this mainly because it has the 3.8 engine which is pretty much bulletproof. Just keep up all scheduled maintenance and the Pontiac will be around for years to come. Make sure the transmission is maintained as well.
My nephew still has the 1988 Bonneville that my wife and I gave him several years ago. We got it when my mother-in-law bought a new car over 10 years ago. He keeps it maintained and it’s past the 250K mark and going strong. As far as I know it’s only had a new alternator and water pump replaced on the engine.