You don't say whether your environment is just a single desktop or is a multiple SAS BI server setup. However in general it is not obligatory to restart SAS after a licence update but it may be helpful to do so as it will ensure that licence warnings in SAS logs disappear, if you are in the warning period for your current licence. If indeed your current licence has expired and SAS is not working, then by definition SAS will only start after the new licence is applied.