I too believe in a pre-trib rapture, but of course it is good to think about what believers might go through if they are on earth during the tribulation. Any believer that would not want to take the mark of the beast is going to eventually have some problems as you foresee.
I don't know this teacher or his background but i think these percentages are correct about death during the tribulation
"2. The places where numbers are given are in Revelation 6:7, 8, and 9:15, 18. The first reference indicates that 25% of the world’s population will die. The second mentions that 33% of the remaining population will die. That means over 50% of the world’s population will die, or at today’s numbers, 3.4 billion would remain. But, that is not all. There are other devastations that are not included in this number." source:
During tribulation, how many people will survive
So there is a lot to navigate if one went fully through the tribulation. The mark of the beast is just one of these things. It likely can't be rolled out all at once. There are 680 million without electricity today. I personally think their mark might be a scar or tattoo. Where there is enough tech though, it will be pretty hard to maneuver and yes, I suppose one could live off the grid for a time. Many see underground barter as possible, but some of course will be confronted to take the mark or die. I do think it is fine to try and stay alive as long as possible, possible one can make an impact on some unbelievers and having some preparation is fine. Either way one has to trust God and not in their preparation.