In the future, will military aircraft supermaneuverability(SM) be sufficiently important of a capability to justify its high expense? Given improving missile tech (e.g. LOAL), won’t most air combat scenarios be resolved before SM becomes useful?

Yes , it will be very important ,because Fgfa vs Fgfa means that both sides won't be able to detect each other until unless they are as close as 30–40 KM ( Based on from how far can f35 be detected by Rafale )to each other , which makes the chance of a dogfight even higher. And not only that ,the missiles of the future are becoming good too , and if your missile evasion systems and electronic warfare can't get rid of a missile coming straight at you ,than you need some tight evasive manuevers to get rid of it . For which super manueverability and a hypersonic speed become very important . That is where jets like f35 will suffer against 6th gen fighters , which will probably all be capable of mach 2.2 atleast and will have supermanueverability . Even India is working on Supermanueverability systems for it's AMCA jet .