The tightening credit cycle (if it happens to any great extent) mostly affects new cars. There is always a cash market for nearly-new (3-5 y/o) cars because cars wear out and these have a good combination of reliability and cheapness. The values might take a bit of a hit, but they will shift.
It’ll be interesting to see the extent to which Brexit affects the UK-Ireland motor trade.
In the last crash a lot of dealers were left with debt servicing problems from overinvestment in premises combined with zero new car sales. A few PCP cars won’t be anything like as bad as that.
In any case, who takes the risk on a PCP deal? Is it the dealer, the distributor or the manufacturer?
edit: I dimly remember used prices going up after the last crash due to lack of supply. Did I imagine that?