There is data on this. It's not really fair to count decolonization as in reality UK and India were always separate countries, linked on a political level into an empire. War costs in the UK took the form of massive debt of 250% of GDP, with really severe austerity for several decades afterwards.

The biggest and longest lasting damage was likely just population loss, which was over 10% in a number of countries, notably Germany, Russia, and all the countries between them.