An Asset is marked "inactive" based on the criteria you've set in:
Manage > Assets > Manage Asset Identification Rules
At the bottom of the page there is an option to set the Asset Activity "Number of days without being discovered before an asset is marked "inactive".
So, if it's not been discovered within that threshold, it will get marked inactive.
Your other questions about the maint. tasks is a bit more complicated... you should check the Maintenance Table in the database. Check the line for:
Delete Stale Jobs
The NextRun, Last Finish and FrequencyInDays hould give you a good idea of how that option is working in your environment.
I think "stale" is based on the # you entered in the option ... if it's 180 days, I think anything 181 days + is considered "stale".
Hope that helps!
I'm still sort of curious as to what a 'stale ticket' might be, and what happens to it.
After 181 days do tickets get deleted? I'd rather they didn't, if they're not resolved.
They're definately deleted.