In 3 billion yrs when Andromeda gobbles us up, (like we've done smaller galaxies for eons), Will earth become a savior or a looter world?

It will be a dead world

Have you done wrong calculations with your usual calculator that is always wrong? It is not billions, but years, that humanity will end up living on earth, the earth as a system will remain where it is and, with God's judgment hell will be inhabited!

The two galaxies will more than likely pass through each other.

Scant change for Earth.

it depends on the Governor of the Galaxy. it could depend on the way civilization could be an army unto evil or an army unto the kingdom of God

We don't always appreciate just how much emptiness there is in interstellar space. Even during the galactic collision the average distance between stars during the event will be something is akin to two bees buzzing about in a space the size of the north American continent.   It's not a zero chance of a collision between them, but the odds are extraordinarily against it.

There is a small but not insignificant chance of our system being gravitationally ejected from the galaxy and flung out into the intergalactic void, there to drift alone in the darkness forever.

All of this is fairly academic anyway. Earth will cease to support surface life within about a billion years from now. By then the Sun will have increased luminosity by another 10% which is sufficient to vapourise all the oceans on this planet and make conditions for surface life near impossible. Nothing will be left to witness the eventual collision of galaxies. Not from here anyway.

Ecc_1:4  One generation passeth away, and another generation cometh: but the earth abideth for ever.

Gen_8:22  While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.

Right now. the Kingdom of Heaven is else where in the Universe. But one day that Kingdom will come down to the Earth. Kingdom of Heaven will be on the Earth when the Holy City Jerusalem comes down out of Space and lands over where Jerusalem is currently. The Earth will become like that of the Garden of Eden. And 144,000 humans will be protected through the Tribulation Period, to repopulate the Earth. All Saints will live in the Holy City and explore the Universe as they so desire.

Neither, by the time Andromeda collides with the Milky Way, the sun will have started expanding into a red giant and the Earth will have been broiled.

When our galaxy merges with Andromeda, if there are any sentient beings on this planet, all they will notice is that there are different stars in the sky. They talk of galaxies colliding but the distances between the stars are so great that the chances of a real collision between two stars is very small.

There certainly won't be any humans or anything resembling a human on earth.. Three billion years ago, the  life on this planet was prokaryotic cells. In three billion years time, life will be as different from what we see today as we are from prokaryotes.