I apologize for the problems and concerns this has caused.
I have restored 32-bit R support to RStudio 1.2 for Windows. It will be in an upcoming patch release of RStudio 1.2 after it undergoes testing and validation. I will also eventually add this support back to RStudio 1.3.
Please note this will still require 64-bit Windows; this restores the 32-bit R functionality, but the rest of RStudio 1.2 remains 64-bit.
For those who like such things, here's the PR on github: https://github.com/rstudio/rstudio/pull/4775