The issue with the empire continuing to have Punjab is that it will gravitate towards its Punjabi territories, becoming a Muslim Punjabi state akin to a monarchical Pakistan. Furthermore, it's an extremely rebellious region, It's a better idea to simply leave Punjab as a bunch of warring misls loosely confederated with one another. In such a scenario, the empire will retain Kashmir, a wealthy region in any scenario due to its textiles being in high demand as far as Central Asia. IOTL, the Durrani Empire faced massive strains on its treasury, and Kashmir can stop that. Also, have Ahmad Shah Durrani announce Timur Shah Durrani as his successor. This should cut down on all of the succession disputes that led to fragmentation.