For long distances and even regional trains there still exist plenty of locomotives.

And BTW, even many high speed trains, including tgv duplex and the acela u nention are effectively locomotive hauled trains.

Yes but the TGV is all based on 70s technology. The more modern trains (such as Siemens Velaro, Alstom AGV, Bomardier ETR 1000) are all multiple-units.

One notable exception is the Bombardier/Talgo 350 (known in Spain as "the Duck" for obvious reasons).

The TGV Duplex was developed in the 90s, and continues to be developed, the new version (avelia horizon) coming out in a couple of years. There's a reason it uses a locomotive ("powercar") concept, it relates to it being a double-decker (which all the other trains you mentioned aren't.

I believe the Acela replacement (avelia liberty) uses powercars as well.

The UK sleeper trains were refurbished recently. They go out of London up to Scotland and down to the South West of England.

They are not multiple units or likely to be if they were refurbished tomorrow. The reason being that the stock is not in 24/7 use. It does the one long night journey then gets parked all day.

The train out of London gets split to serve different bits of Scotland, so you do get some shunting around going on when they do things to the train.

It doesn't go that quickly as a train because there is no need. Being in Euston at 5 a.m. is no fun, might as well be there at 6 a.m. with some sleep had.

So the loco that pulls the train can be any old freight thing. Although now it is likely to be a Class 73 diesel electric that can use electrified track as well as diesel. Note that there i no electric track all the way out to Scotland.