I don't think anything could shake my faith in God. To be honest I would not be surprised if so called Aliens showed up one day. My question would be then who are they REALLY? Should we immediately beleive everything what they tell us? It depends on WHAT they tell! If what they say contradicts with the Bible then I would think they are Demons and Fallen Angels in reality and they are part of the big deception of Satan.
I have already heard theories that the Human Race was created by these Aliens and they keep coming back to check what's up with us and to show us the "right way" etc. Now these theories only seem to be thoughts of marginal groups and cults but they can well be the bases of a new religion - especially if these "Aliens" once show themselves to the whole World and claim the same...
In that case it would be difficult not to beleive them! Just imagine! They land with their spaceships, get out and claim "We are here to save you" and CNN broadcasts it live. At the same time they would also claim "there's no God, there are only us, Aliens - we have created you".
That would be the perfect deception. I can imagine only very few people would NOT beleive them after such a spectacular and convincing arrival!
Even many Christians (who are weak in their faith) could be deceived in that way!
I am not saying this will be the case. Maybe there's really nothing in it at all and maybe the people who think to have seen UFOs are all mistaken or/and liars, fools etc. But this is also a possibility and I think we have to be ready to stand strong in our faith and never give it up even if the majority of people give it up because of some kind of deception like that and even if we are made to look like fools in the World's eyes just because we stick to our "old faith".
BTW, I think that will be one of the tricks of the Anti-Christ to discredit Christians: he will make us look like fanatical fools, he will ridicule us.
But keep the faith and NEVER give up WHATEVER happens!