I only ask this given the track record of the shop provided in your first post, but are you sure the puddle of oil under the exhaust they described is actually a puddle of oil and not soot/condensation?
Personally I would, as others have suggested, take it to another shop and start over, and follow the advice already given here.
I'd also make sure the battery and glow plugs were functioning fully, even though that seems really obvious and would not explain the highway failure you had. If replacing the IP and ALDA helped anything, it still might not start if you had coincidental GP failures or a half-dead battery. Just a thought.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)