what would the risk assessment be if Belgium would spit ?
Just simple, you can't even start because there are so many unknown factors and so many things that would take years to negotiate and so many scenario's with so many different possible outcomes that the balance could tilt totally in the direction of 'don't start what you can't end.'
Belgium is not tsjechoslavkije. The economies, transport and public infrastructure are much more intertwinned than was the case in tsjechoslov. There is one capital Brussels that brings in billions of Euro's each year for both regions because it is an international diplomatic capital. Playing with Belgium and losing Brussels would have immediate effects on every region. The unknown factor is if the European Commission and the hundreds of other organisations and institutions would stay if Brussels was to become 'independent'. This would not be up for the ex-belgians to decide. Can you imagine Brussels without European institutions ? Half of its center would be a ghosttown, real-estate prices would crash and employment would follow, because there would be no strategic reason for all those headquarters to stay in Brussels.
The social security, health care and pensions are another factor with which one can't play without making a risk assessment. And when you note the risks, you will see that the only effect would be that the risks would afterwards be distributed among smaller populations that would be more vulnerable to demographic trends, privatisations and epidemics. Do not forget that Flanders will have in 10 years from here a population that would have more pensioners and older sick people than the other regions.
And there are so many other risks and unforeseenable events and scenario's that the old rule of IT should come back to politics.
Do not fix it if it ain't broke
Just patch it a little here and a little there. And go on with the work you were elected for.