Even though mulit's have been getting better, including hybrid gas/electric ones, I think that copter still won't be feasible for running in the OBC because of the range and speed required. Ideally the avoidance action would be a navigation event, not a failsafe event in the case of the OBC. Hovering in a position will probably not be viable in the OBC due to the time constraint of completing the mission in one hour, and diminishing range reserves trying to hover a VTOL/quadplane whilst waiting for a no-flyzone to pass. In fact it's possible that an encounter with the dynamic no-fly-zone might result in mission termination due to running out of juice, especially on airframes that are "optimized" for the range/speed and not for hover. So a predictive type of avoidance would be preferred I think, with the best resulting course plotted depending on the variables of weather and all no-fly-zones/geofences. Apart from the first two WP's it seems we have some flexibility in where we fly when on the course, so we should have enough room to move around obstacles.
Funnily enough when I first started with quadplane development, before either PX4 or Arduplane supported it "ages" ago in 2013, I actually ran Arducopter on a PXH and strapped a pusher prop to the back of a mini hex and raced at 100kmh around the sky! I used a separate RC channel to control the pusher thrust. It worked a treat! The interesting thing was that even without wings on it at the time (Skyfun wings were added later) the overall current didn't change much between hover and forward flight with that setup (maybe 10-20% more).
This was due to a higher pitch forward prop pushing a flat profile hex horizontally through the air instead of on angle, which meant the hex props would autorotate in forward flight resulting in less hover power required to keep it airborne. At first controlling altitude was a bit of a pain until I switched to alt hold, which basically turned the thing into an high altitude hovercraft with it drifting around the sky on the pusher prop motor and only using yaw to control direction. You'd just flick the yaw in the intended direction and use the pusher throttle to control the rate of turn, and just drift around. Using roll and pitch for a roll type turn always ended up with the thing changing altitude and hard to control. Was fun! (I have to get it out again) Afterwards with the wings there was a only a slight difference in current draw, but the thing would always climb with throttle as it had too much lift from the autorotating props and wing. We're working a variation of this for the next event, that is basically a 50g blob of custom made avionics with a few 18650 batteries held up by a minimal wing, propelled by three motors with asymmetric lift for hover and only using two servo's, all in a hybrid tailsitter/quadplane config under 2kg.
In fact it might be a contender for the Japanese competition provided you can return to swap batteries or fly more than one aircraft. 3km radius is a big area to search in detail with undulating terrain. Do you have a link to previous Japanese Challenge pls? Also when you say retrieve Joe, do you mean physically lift him up with a drone and bring him back to base? Now that is a challenge!