I am almost a 100% sure they will be saved somehow. Either another marine drops by and intervenes (smoker?), Gap will get up or ajoki will save them with the argument that they are worth more alive than dead. Keep in mind that garps status and fame is quite important to the marines and by some extent to the world government as it would be a big blow to their reputation if garp would be killed, so I think they could use them as bargaining chips and Blackbeard always has a bigger goal as he is quite cunning.

I think it works perfectly for him. He is still very naive and humble but his heart is in the right spot, kind of like Luffy used to be/still is. Thats why he is the future of the marines, he will grow more formidable but at the moment its just his core personality which is still in the making.

Despite that, the island seems to be full of heavy hitters so I think he holds himself quite well.