Will Laserjet toner cartridges dry up if the printer sits idle for a long time?
No, you needn’t worry toner cartridges will have the issue sitting idle for a long time.
Firstly, the toner are not liquid but powder and it won’t plug the nozzle like ink cartridges or have the tendency to dry and harden. But you should also be aware that toner cartridges be stored appropriately. It’s easily be affected by high humidity or heat adversely in different ways. The toner could get fuse and “clumpy” which will result in negatively impacting on the Electro-Photographic process; Don't remove cartridges from the black plastic wrapper until ready to use them. There is a photoconductor in the cartridge that is sensitive to light and can be damaged if left in the light. It can also affect other components such as the developer roller as well if sitting too long.
Secondly, If warranties are a concern you will be better off buying a high quality product as the they will be guaranteed several years...while the OEM warranty is typically no more than 90 days.There is no time limit on the HP toner warranty; much less only 90 days. The toner cartridge is warranted against defects until it is messaged as “Low". At that point, the cartridge may still have usable capacity, but HP no longer guarantees that it will be flawless. You may see print fade, or color balance changes. If those are acceptable, continue using the cartridge as long as you are happy with the results.
One of the main advantages of LaserJet printers over ink printers is their ability to sit for several months and then print without issues.