The game closing with errors is due to bugs, but that should work normally. The engines are now saved continuously, as are the cars. So you can quit out any time even if the thing you are working on is not done yet. That should be much better than before. If you want to work on your engine but are not sure if you want to keep the changes you are going to make, just press the hold button. If you want to keep it with the new stuff, press the hold button again, if you want to go back, click revert.
Honestly, I don't know how anyone would like the old system better, UNLESS they don't fully know the new system yet

takes some time getting used to.