It'll go well for a while but then the usual/inevitable thing will happen. That is, once things go wrong or once Chelsea go on a bad run of form, Abramovich will have a few (angry) words. I'll give Di Matteo, at most, a season and a half.
Maybe Abramovich is only looking for someone to keep the seat warm for 12 months before seducing Pep...
Hmmm, very plausible...