Term for a guarantee a manufacture makes that a product will be produced for a number of years?
Longevity.

Examples:


NXP
ST


It is especially important on digital components. You can exchange resistors and capacitors without problems, but digital parts require design and qualification.

Often a last-buy date is given. Before which you have to order your last batch. Keep an eye out for, or register to notifications of Product Change Notes (PCN). These will tell you when and how parts change. (eg: different plastics, different country of origin, new process)

Recently many semiconductor companies have merged and split. (atmel, nexperia, microchip, freescale) Often they will shuffle their assets, and those are production facilities. Expect PCN's after merges and splits.