Life expectancy of inexpensive cards [?]

Depends!!!!

depends on who assembled the card depends on who made the caps, the resistors, the chips depends on the heat levels outside the computer which inturn impact heat inside the computer depends on how well isolated the backplane is from the power in the wall

Depends!!!

fundamentalism, fundamentally wrong.

Usually until the warranty expires.

So far, I haven't seen any failed PCI wireless cards out of about 25 or so I deal with in various systems. The "failures" are upgrades inspired by buggy drivers, 802.11b only, and security upgrades. There's very little power dissipated in the radio section so meltdown is unlikely. Basically, they'll last as long as any typical PC plug in card.

A few cards have MTBF statistics which might be useful to estimate the life expectancy. I'm too lazy to Google for that.

Are you expecting a failure?