I think those >13yr old soldered Pentium 4s and Ds are running just fine out there. Same for all the 10yr old C2D E6xxx, E8xxx, Q6xxx, Q9xxx, and more recently Nehalems and Sandies.
Cedar Mill Pentium 4/Ds are 81mm², Conroe is 143mm², Wolfdale is 111mm², Nehalem/Lynnfield are 263/296mm², Sandy is 216mm²... not to mention the EP and EX versions of the latter two, Nehalem-EX is a 684mm² behemoth. There you have a mix of small and big dies throughout the years that have been soldered in the past without much issue, in many different packages.
Have you heard of any of these outright failing? It was most probably caused by a heatsink completely full of dirt and neglect.
What you had in the past was TIM in the lower end processors like E2xxx, E4xxx, E5xxx, E7xxx, Q8xxx C2Ds... the higher end models were soldered. Hell, Intel knew why they soldered Clarkdale's CPU and left the MCH+GPU with a thermal pad. I mean why even bother with solder here? Performance reasons..? Sure, this is probably why we started seeing >4GHz overclocks on Clarkdale when it came out, and it would only get better with Sandy.
That 32nm node was awesome! Those processors wouldn't have been so popular if they were TIM'd. You'd probably not heard of 5GHz stable done on Sandy silicon lottery winners without delidding.
Reliability isn't a problem with soldering in the time spans we're seeing so far (15yrs at most going back to Pentium 4/D). Money, materials and bean counting are, starting with Ivy Bridge back in 2012 and these concerns lately being stretched to the point of being ridiculous with Skylake-X. Some points der8auer raises in his analysis are... doubtful. It's a great piece nonetheless. Is the material stack needed to solder seen in der8auer's piece in short supply? AMD seems not to think so, as they've been soldering non stop since A64 came out and Ryzen is soldered. Sure Intel handles much more volume, but still.
It was alright when the high end models were soldered and the cheap stuff wasn't. This is a move that probably makes sense for them in the financial side of things, but on the other hand and going to a more recent example... the heat produced by those AVX512 units would pretty much prefer solder to TIM in whatever environment those processors are deployed in.