Hey, Peter. I think it means that they would be together 'forever' until one of them dies of old age. I do not think it means suicide.

Without more context, it's impossible to say. It could mean he's in danger and expects to be killed and anyone who stays with him would be killed also. If it's a love story, maybe he means they would be together until the end of their lives.

就是一起老死的意思吧。

Susan rightly said it may also ne vice versa. S'ppose a girl is saying to his boyfriend that if you don't leave me, we would die together as her father is from underworld. Nice story, indeed.