What is the lifespan of a SLA Resin Tray?
It depends on tray and resin type you are using.

PDMS

If you are using PDMS (eg. sylgard 184) coating for your tray. (B9 and similar printers using this type of tray). 

Life of tray PDMS coating depends mainly on:


How long you print without breathing floor.
How reactive is your resin.


You could get 2 3 prints up to 15 20 prints.

It is suitable for printing delicate pieces.

FEP

Large number of manufacturers using FEP.

Life of tray largely depends on.


Thickness of FEP
Piece sizes and movement speed during early layers.


Usually you could use same tray for couple of hundreds of prints. 
Optical quality is not comparable to other alternatives but without human error factor you could get almost unlimited prints. Delicate pieces require tough resin.

Teflon

It is halfway between PDMS and FEP.

There are other tray alternatives:


Envision uses special glass you could print on average 50 prints.
Carbon 3D uses super expensive oxygen-permeable window.