When discussing this type of issue, people often fail to grasp that the question “Is there a God?” is not equivalent to “Is this/that/any particular religion true?”.
Would life on another planet be problematic for lots of established religions? Definitely, but then as others have said, they’ve managed to survive over a century of withering scientific discoveries. It’s hard to see this being the one that finally kills them off.
Does life on another planet have any implication for the question of God’s existence? I don’t personally believe it changes anything. From an empirical perspective it’s already a fairly pointless question, but as long as the door of possibility remains open I think religion or religious experience of some sort will continue.