The code for all packages on CRAN is open source, just like R. And enough organizations have invested enough time and money in R that I doubt the tidyverse will be abandoned anytime soon. If Hadley and R Studio vanished from the Earth, somebody else would take over maintenance of the packages.
This goes for all packages on CRAN. If a maintainer ever leaves, you could (a) hope somebody else steps up as maintainer, (b) fix and share the code yourself, or (c) contract programmers who fix and share the code.
Also, what do you consider "Rstudio packages?" There are very few packages that actually require Rstudio the IDE or Rstudio the company, and most people never program with them.