If a subcontractor does NOT file a 20 day preliminary lien, do we need to get a lien waiver from them in order to release their check?
Obtaining lien waivers from everyone on the job is the best way to make sure that everyone's been paid and that no liens will be filed on the project. While it's true that failure to send a preliminary notice will upend lien rights in Arizona, it's still best practice to collect waivers to ensure that no disputes will break out on the job. After all, a payment dispute of any kind - beyond just a mechanics lien - could negatively impact the job, a GC, and an owner. Of course, with all of that being said, it's not absolutely mandatory that a waiver be collected in order for a check to be cut. So, if a payor is comfortable providing a check without a lien release, they can do so.
For further discussion on collecting waivers: How To Handle Requesting & Tracking Lien Waivers.