Depends entirely on the why and how.
If it's through something like the Union of Arras/Atrecht being agreed on with more provinces(or even all), the net effect is that Spain loses just as much (as it'll make the Netherlands near-useless for Spain), the Dutch gain even more (since they can now freely expand under the Spanish aegis).
If it's through something like a historical Arras followed by serious Spanish victories, followed by minor concessions in the north, they might seriously benefit by exploiting the North - at least initially.
If it's by crushing victories before the rebellion gets anywhere, the net effect is probably less positive, as there may be decades of discontent even after Spain wins.
In all cases, I consider a third 'habsburg realm' in the Netherlands (as Albrecht of Austria and his wife had in the early 1600's) likely in the long run.