Probably massive inflation for Russia, high unemployment, probably need a country like china or even India to loan them money. For us, unless you hold Russian debt, nothing much.
They’ve already proactively limited inflation by doubling interest rates to 20% and requiring Russian energy companies to convert oil export revenues into Roubles. Russian debt has already been downgraded to junk status in anticipation probable default. If anything, official default will hurt foreign bond holders who can’t buy more Russian debt anyways due to sanctions. At this point default will probably hurt global markets more than Russia. However, if oil prices continue collapsing (they’ve fallen 30% from peak in the last week), that will hurt Russia more than anything.