Russian lives have already been lost in Syria, how many, we don’t know. What we do know is that the Syrian people (generally) are extremely grateful for the Russian support. It has been vital to the survival of areas such as Deir Ezzor, both on the military and humanitarian level. There is no safe way to land at Deir Ezzor airport any more, not since the US in conjunction with ISIS attacked Syrian forces in September 2016. Subsequent ISIS control over certain areas now means that the Syrians cannot fly in vital supplies safely. Deir Ezzor has been cut off from the rest of Syrian government held areas for over two years, so the actions of the US coalition were catastrophic. ISIS have repeatedly attempted to defeat Syrian forces in Deir Ezzor but fortunately for the 100,000+ civilians, they’ve failed so far.
Despite serious risks of being shot down (the US/allies have supplied terrorists with manpads) Russian pilots have been dropping tonnes of supplies to Deir Ezzor, without which the town couldn’t have survived this siege.