Heat won't kill it - just make it old (go grey) before its time.
All developers need all of their component parts to work properly. In some cases, if you miss something, it won't work at all.
If the job of the baking soda/washing soda was to change the pH to a range that permits all the rest of the components to work (i.e. to reduce the exposed silver halides), and the soda doesn't do its job, the rest of the components may not have been able to do their jobs.
If the exposed silver halides aren't reduced by the developer, then the fixer will just remove them from the film.