He's not really dead, you know.
Everyone changes jobs frequently these days. Five years is a lifetime in even an average job, far less a job so technologically driven as F1. Most of us know that to get the big money, you have to change jobs; and many times the new employer will offer extra enticements that your present employer won't match. Not abnormal at all, just that we notice when there are several from one location. If Renault has a BAR type first year, the defections will be legion there too.