At this point it's reasonable to expect the air and the mini to come at alternate years, air in 2022, mini in 2023 and so on. Mini is not going anywhere. There was a reason why they waited so long between the mini 4 and 5, they explained it in an interview some time ago, but the mini is definitely part of the line for the foreseeable future.
The base iPad will remain on a yearly cycle, while the pro should be on a 18 month cycle and use the same chip as the Mac (which aligns with expectations of a M2 coming in fall 2022, no earlier).
The air will probably move to 128GB storage and 6GB RAM. Unlikely to get a better screen, at least until the 11 is updated, which will be next fall, unless they are released at the same time.