Philip III had two sisters Isabella Clara Eugenia married with archduke Albrecht of Austria and Catherine Michelle married with duke Charles Emmanuel of Savoy.
Both had issue, however IOTL the children of Isabella & Albrecht (Philip, Albrecht and Anna Mauritia) all died young.
The Habsburg Netherlands in this scenario would return to Spain, just like IOTL when Isabella & Albrecht didn't have surviving issue.
I don't see drastic changes with OTL, but a surviving Spanish branch of the house of Habsburg, which could prevent the war of the Spanish Succession could in part be good. However some of the problems faced by Spain (at this point the Spanish Kingdoms) were caused internally and not (only) externally.