The saga:
Day one; will not start, a jump start revives it.
Day one, later; Key will not disengage from the ignition.
Week one; ignition switch replaced
Week one and a day; started enough to inspire confidence, then crushed a Saturday with stranded no-start, but will turn over, with apparent pressure in the fuel line when gas in engaged.
Week two: the service e center that replaced the ignition switch tries different key and it starts, hold a week to find problem, and can not.
Week three; car is back and going and fails to start
Week three, and four; At Volvo dealer ship, replacing the fuel pump does not do the trick, relays are said to check out. The dealership gets crazy are submits a request for authorization for a new “electronic control unit”, but will not certify that this will provide a fix. I get crazier and approve work.
Week five, still will not start, and the Dealer is out of ideas. A this point any ideas that lead to solution will be rewarded $$.

If you dare to enter the sage I will be very thankful and rewarding. The downer is currently CA bay Area.

The jump fixing it one time, and the key fixing it another time, and the problem you had with your ignition, really leads me towards the immobilizer reader coil. Does your car have a green ring around the column where you put your key in? Most 98's do; some (a few) early 98's don't. The part number is 9442961; list price is 49.18. The car will sound like it is trying to start, but you won't have spark or fuel...

Chris

What year is this S70?

This S70 is 1998

Cam position sensor? (Search on that to see if other's problems
with the cam position sensor match your problem.)

Dealer claims to have already checked the Cam sensor!

Is the dealer telling the truth?

you mean about the cam sensor?