Eh, it's not like this is the first time people have enter the presidential race and then not make any headway and drop out, only to get a job in the administration later. We saw that with Ben Carson, and Rudy Giuliani respectively.
Sometimes, you run not because you want to be president immediately, but because you want to make the actual front runner aware that you'd make good VP or Secretary of State, or AG, etc. material.
That said, Beto has a way better chance of winning the Democratic nominee than say, Kristin Gillibrand, or Cory Booker. Fucking Julian Castro is still running, and all that literally has is that he was running HUD at one point. I'm trying to find out what Castro's been doing since 2016 and apparently, he's just been running for president all this time. There's no reason why Beto can't run with this gang of misfits until near the end or at the end, however it shakes out.
I get it that some people would rather see Beto run for the other senate seat in 2020, but John Cornyn just a regular Texas Republican vs. whatever fuckery Ted Cruz is. People don't outright hate Cornyn like they do with Cruz, and I don't think he'd make any headwind against Cornyn in 2020 like he did with Cruz. Beto probably has a better shot at being president then he does at taking Cornyn's senate seat oddly enough.