I expect things like minefields will be removed but plans for re-emplacement kept on the shelf. Lots of surveys will be done for rapid emplacement of obstacles, but the ones in place will probably be removed as hazards for normal commerce in most places. Most of the emplacements will not be manned, but maintained adequately (hey what are slave laborers and corvée labor for), major emplacements will be manned. As tome passes after the war, the refurbishment updating of emplacements and the potential building of others will depend on the international situation. If there is a low level war going on like AANW, then you'll see a higher level of construction etc. If it's more like the OTL Cold War, then not so much.
A lot of the major installations have held up pretty well even with no maintenance in the last 70 years, heck even Maginot lines structures are not crumbles 80-90 years later. As long as maintained, you could put guns back in, redo command bunkers etc relatively quickly as long as you had plans for it and stored materiel - think of it as a REFORGER type operation for the Atlantic Wall.
As someone with targeting experience let me say that the reinforced concrete bunkers of the OTL Atlantic Wall will stand up pretty well to aerial bombing, not as well to naval gunfire. Until you get the sort of precision guided munitions we have now, using conventional bombin is not going to be terribly effective.
IMHO the minimum is sort of low level improvements updating for key areas, chokepoints etc. Beyond it all depends on the perceived threat. Any attempt to invade continental Europe can't be secret - the exact location yes but the buildup no - so most of the fortifications can be left empty and checked periodically, and filled up with manpower when needed.