Not impossible to get rid of TNT Air, but not as easy as made to be either.
TNT Air has, and uses, cabotage rights, and rights to points beyond Europe set in bilaterals that depend very much on the nationality of the carriers involved. UPS may need TNT Air to keep a 777 or two to fly to China or India or Russia... It can be tricky, just ask DHL. They still route their LOS flight through BRU because they can't get the rights transferred to LEJ.
TNT Air has a deal with the regional government (LGG owner) running until 2036 for incentives and preferential terms. UPS can still close TNT Air overnight, but it will cost some cash.
CGN cannot handle the TNT volume even with current expansion work, and I don't think (could be wrong) that UPS has enough spare air capacity to handle it either. So unless UPS has a magic wand to double CGN and a bunch of aircraft parked in the sand, it will need LGG and TNT's fleet at least for several years. I can see the 146s gone soon, but the 737s will remain and be augmented with a handful of 757s.
If you are keeping score, there's a sure US victim already. The ABX/ATI (can't remember which) flying for TNT will most likely end ASAP.
Much of our intra-Europe flying is actually a "change of gauge," where our larger MD11 and 744, fly into our Cologne hub from Asia, the Middle East, and North America, gets sorted and delivered to points beyond on our "smaller" 767 aircraft
A not-so-insignificant detail many seem to miss. UPS' European network is optimized for Europe-ROW traffic, the larger share of its current business. Buying TNT gives UPS a massive boost in its intra-Europe operations and it may need to make significant changes to its network. It makes predicting the future of TNT Air that much more difficult.
But I can clearly see an upside to FedEx and DHL in this UPS deal.
Which one?!? Right now, DHL is out of reach at #1 in Europe. Combining UPS and TNT gives them a (small) chance to fight for #1. FedEx is already marginal and will be even more so.
Expect DHL and FedEx to try everything to block this.