Well you have several options to consider. If you do not get any acceptance this year and you applied to all of the TMDSAS schools, you would be considered a reapplicant and thus would have to show improvement in your application overall. Honestly, I don't think the reapplicant deal isn't as big of a thing for Texas schools as it is everywhere else.
If you don't get accepted and do the Med Sci program, then I would recommend you not apply again while you are in the program, since the entire reason for the program is to improve your grades. If you apply while doing the program, you won't have enough grades to show them before the fall is over. That would mean that you would reapply two years from this cycle. I just completed the Med Sci program this year, and if you are planning reapplying two years from know, I would recommend looking at other, more formal Master's programs, like Texas Tech's. Theirs is a two-year program, but the students apply to medical school during their second year. It is much more selective however. So this would be the exact same timeline, except programs like Tech's are affiliated with MD schools as well as much more well-rounded.
So at least for this cycle, you might as well add all of the TMDSAS schools if you don't mind writing a couple more essays and paying for a couple more application fees.