They get you out, most often by you reversing out, or into a turn around area. Sometimes they push you out at the top. In rare cases they pull you up on a winch or with modern 4x4. All depends on the hill and weight of the stricken car. They are interested in clearing the hill for the next man, so its in their interest to get you on your again.
The VSCC run 7 trials each year. The hills, usually about 12 or 13 are scattered around a 20 miles radius (ish) and you visit them as you wish throughout the day. All the cars are prewar.
Each hill scored 1 to 25, get as high up as you can.
Some are bumpy, most are muddy. If they get rough for you, you just slow down. But the serious boys just keep it lit (full chat) all the way, conditions permitting.
VSCC.co.uk shows you a lot.
I do all my trialling and other speed events in the VSCC so this is my preferred club.
The PreWar Austin 7 club run the Butts Quarry one – I’m not sure if others too?
The Clee Hills trial is good I hear in South Shropshire, but I’ve not done it yet.
The MCC do 3 trials each year. Theirs are pretty tough. They cater for prewar up to modern cars.
The Sandracer has climbed the Drumhouse (with previous owner) which is a slate quarry road rising up Fleetwith Pike from the top of the Honister pass in the Lake district.
Descent of Drumhouse is on a tow rope for 2 wheel braked cars such as a Jowett, as the drop off into the valley is a little dangerous.

Concours in a field has its place, trialling too.
I plan to turn up in a standard car, very close to factory specification, and bimble round and have a jolly time. Most trailer their cars there, but for me, if the event is close enough I plan to drive there too.
I also do speed hillclimbing in another type of prewar car and take that very seriously indeed.
Different strokes for different folks and all that.