There are 5.5 million names in the Democratic Party VAN. That's the number of voters the GOTV campaign is going to attempt to reach in the month before the election. Likely voters might constitute only about half of that number. So if total turnout is ~5 million as you say, Beto wins this thing going away if even a small fraction of the intended GOTV targets wind up at the polls. Realistic turnout will be in the 7 million range, approaching 2008 numbers, including more Republican voters than normal.
https://betofortexas.com/plan/?source=texting
So, no, 200,000 libertarians are not the focus, nor should they be.
I was on a organizing conference call this past Saturday (I think by mistake) with a couple hundred new volunteers, mostly from out of state. About half planned on flying to Texas in the few weeks before the election to block walk (no shit) and much of the rest planned on phone banking. Maybe most of them don't show up, but we could be in the midst of a historic GOTV effort starting in October.
If the Quinnipiac poll tomorrow shows a tie or a small Beto lead for the first time then the sharks will smell blood in the water.