Well, it's quite unfair as certain heroes like RockeY mentioned
are able to take on 3 - 5 players alone, especially Naix, Phantom
Assasin and Terrorblade when they have the proper equipment.
If the last player is going to be someone like Lich or Zeus (people
who can't run, no disable), who the heck is going to care? Even if
they had infinate money no one is going to be scared of them. Just
gang them and they'd die patheticly.
On the other hand, if it's a late-game hero (must have healing)
like any of the 3 which I mentioned above, the other team is
probably doomed. For example, Naix with his gay 40% lifesteal can
probably just go around biting everyone up while the victim's
teammates try but fail to kill Naix.
And yes, it is possible. Sometime ago I was playing Terrorblade,
and my teammates were getting owned upside down so they all left,
and so I took their items, pawned some of them for cash, and in the
end I had Treads, S&Y, Aegis, Rapier, Skadi. I tried to fight
their team, but lost because I got disabled too much, and their
Naga Siren burned away all my mana. After that I farmed abit more
and made a BKB, fought all 5 of them again at the river, they lost
very badly and quit (didn't even sunder).