We don’t know Roy’s AC, so some analysis will cover several Ac values. We don’t know roy’s level, but we’re going to assume 5 hit points per hit dice and a +3 con. At level 10, that’s 80hp. At 15, it’s 120hp.
A mook is assumed to be have 1HD and +1 Base Attack Bonus. A Mook is not assumed to have any feats or class levels that would improve on this. A mook will be assumed to have a strength bonus, and we’ll examine the effects.
At 20 ac, a mook hits 10% of the time (19 and 20; 20’s always hit). A good strength score - we’ll assume a Mook never gets above a +3 bonus - bumps that to 25%. With a single attack each, 8 mooks surrounding Roy will hit twice per round. They will do in the neighborhood of 1d8 +3 damage, or 8.5 on average, and 17 damage per round. Level 10 Roy dies on the 5th round, on average. 15 dies on round 8. But 20 ac is trivial, and we might have given the mook too much strength. The important takeaway here is that this is probably a mook’s best case scenario.
At 25 Ac - (by the way, that’s +3 full plate and +3 ring of protection, with no dex bonus), a Mook has a 5% chance of hitting Roy, only on the famed “natural 20”. The average damage per round is considerably lower. I am too lazy to remember how to calculate the average number of hits per round on 8 guys each with a 5% chance to hit, but this is less than 1 hit per round. The important point here is that there is always a 5% chance to hit Roy. There are ways to mitigate this - Damage Reduction - but Roy lacks them. Dr 5/magic would massively reduce incoming damage. Dr 10/magic would reduce all incoming damage except on crits. The problem Roy faces here is that every hit becomes a threat (fortunately, that means someone has to roll 20, 20 to succeed; very unlikely). This is a weird quirk of the tabletop crit rules, which I really don’t think favor players but players apparently love them (and it is possible to do crit focused builds on the table top, where you get them a lot).
Off hand I know of no fighter feats to help Roy here. Certain Pathfinder barbarians could stand for a long time inside something like this though (the Invulerable Rager archetype gets Dr 13/- at level 20. Meaning that only a confirmed crit would ever harm them; but they would get like 60 rage-induced rounds of “let me pounce full attack pods of enemy soldiers over and over!”. That would be kind of hilarious).
Naturally, there are people shooting bows and there are people with polearms (reach attacks!) so Roy can potentially face many more than 8 attacks per round. A mook archer probably only does 4.5 damage per round (Longbow is d8, we’re not assuming anything fancier), and while a mook archer would face all sorts of stiff penalities for shooting at Roy while Roy is in melee, there’s always that 5% chance to hit him. A high level fighter is less durable in this situation than you might think. Even at 20th level, with max hp and a +5 con bonus (300 hp), a fighter would go down inside of 30 rounds without healing or damage mitigation of some sort. And potentially very quickly. Technically, I don’t think Roy can move and great cleave in the same round, but I may have that wrong. And this isn’t the tabetop. Roy could kill a lot of guys in one round potentially, but not enough to win without outside help.
Naturally, a high level divine and arcane spell casters can do all sorts of fun things in this situation. But. . . yeah.
