This is what is going to happen

Russia will blame everyone and use the usual whataboutism arguments, we already had Russian ambassador on CNN yesterday trying to float conspiracy theory that US done it because Russia destroyed all their chemical weapons and US has not (i kid you not)

Sanctions will be announced by western countries, but not implemented (whatever dirt they have on Trump must be good)

Everyone will forget and move on

Few years later proof will be found, but by that stage no one will care, case in hand Russian antiaircraft technology "falling" into rebel hands and shooting down a passenger plane a few years ago.