Once burnt, yes, safe greenhouse gas. At least, no worse than any other combustion products. I mean, it would be nice if hydrogen wasn’t such a pain, but we have to work with the universe we are given.
Methane leaks need to be contained to the amount practical, but they are doing that.
No. It is part of the space treaty that most nations have signed up to, that any part of a space craft remains the property of whoever launched it, and clean-up of it is the responsibility of the country from which it is launched.