Is it wrong for me to expect someone to teleport into a fight?

So in my last game we had a Gangplank who pretty much just afk farmed top the whole game. One fight in particular though we really needed him and he didn't come, even though his teleport was up and the enemy top laner had roamed mid to help. There was an infernal drake up and a fight breaks out in the river. Gangplank ults to assist us, but just keeps on farming. At the end of the fight we all die except Gangplank, but we end up killing 3 of them. After the fight is over they're able to get the infernal which puts us in a really bad spot the rest of the game. Later on they're able to get a second infernal and we eventually lose. I'm 100% sure that if Gangplank had actually come to help us that fight would've gone differently. Is there really any excuse for him not to come? If there's anything worth fighting over it's an infernal. That's not something you just give up without a fight.