Have had this desk chair for about 30 years and with a bit of effort it'll easily last another 30. All the mechanics (rolling and tilting - pretty simple) work fine, just need to reattach the two pieces and possibly add some bracing underneath the seat.
This same type split happened a few years back with the right side and the chair has been stable after gluing it back together but the seat is constructed from 5 planks and only the three middle ones are supported by the metal chair mechanism. I'd normally criticize the design since the arm rests are attached to the two outer planks but it did last more than 20 years before having any issues which doesn't seem like a reasonable expectation for any desk chair you could buy new these days.
Let me know when you can stop by to pick it up and I'll provide the address and put the chair out in the driveway.