Are on-premise firewalls still required if I move to SASE?

It depends on the desired architecture. On-premise firewalls may remain to be used to simply ensure resilient access to SASE services through SD-WAN or may used for LAN segmentation in support of the wider security architecture. Typically requirements for on-premise firewall are greatly reduced which will save licensing costs and management overheads. In some cases only a router may be desirable.