Between the two choices, isolation is obvious. Nobody wants to be responsible for the creation of World War III and thus we must find ways to avoid direct armed conflicts with military superpowers such as Russia.
Actually, that's why Russia and the USA have been engaging in proxy wars for decades. To avoid fighting each other directly and thus using nuclear bombs.
So far, since the end of WW2, history has shown us that countries which are isolated with punitive international sanctions end up being severely crippled. They can't use excessive force because the rest of the world simply won't let them have what they need to do so. They can pretty much only bark, not bite. Of course, they will once in a while engage in small conflicts, but nothing that would reach a WW3 type of scale. North Korea, Iran, etc. are good examples, so far, of the viability of isolation policies.