Apart from inflicting casualties in Syria ISIS can arrange some acts of terror within Russia or to Russians outside it.
You mean again sending troops abroad? Russia can't digest what it brew in Syria, so it will hardly extend its Middle-East operation into Egypt as well.
Russians make the population of Russia, so eventually Russia is a sufferer. But you are probably right in believing that sufferings of a small group of Russians are not a great concern of Russia as a state.
And in terms of retaliation, it is a question who is expecting one - ISIS has been under attack (as Putin claims) so nothing is likely to change for it. It is Russia which is in for more fun.
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