What is the typical procedure if an engine fails during a vertical takeoff?
F35 and Harrier are both single engined. Both  had a forward fan providing lift through this fan, and in case of Harrier forward nozzles turn aft for thrust. F35 it provided lift only.  Aft nozzles in both types vector to give lift or thrust. In Harrier all nozzles are synchronised, 

So silence from the engine means it's time for the black and yellow handle.. If a twin engine e VTOL aircraft where lift is provided by both engines and one has a failure, then again until you transition to sufficient aerodynamic lift you are going down... But also probably rolling away due to non symmetric thust. Look at design of DornierDo31. You can climb I side on at the Deutches  Museum at Oberschleissheim near Munich.( I was Senior Systems Engineer on Harrier, Sea Harrier. )