If Bernie does not run, yes I can see it.
But Bernie certainly is running.
That's why a VP pick would be a perfect pick. Continuity.
I think Sanders' stock has petered out a bit in over the past year. He is still of course the standard bearer for the policies he has mainstreamed but it will be increasingly difficult for the country elect a 79 year old potus when there are younger candidates entering their respective political primes who are generally promoting similar issues. This is why I think if there is a viable younger candidate, they will likely take the mantle from the oldies.