My work vans have pretty high miles. 300+k on the ford with the 4.9,the 5.8 had 300000 when the odo died last year,the cube vans have over 300k on each,and the Chevy got sideswiped the other day and totalled and iirc the 5.0 has over 400k.
I've absorbed my dads trucks in my youth. An 89 dodge with a 318 had 450k before repair was more costly than replacement,however the engine ran stellar,the rest of the truck was falling apart.
Then I had a 96 ram with the magnum 318 that had over 450k,very hard miles too,before I got sideswiped at a stoplight which totalled the truck,the engine ran great though,but went through 2 trannies.
None of the examples above were ever opened up,still had the original gaskets.
My girls windstar has 350k,my 99 silverado has 275k and is my winter truck,my C3 has 200k,maintenance unknown since I just got it.
My 2004 ram hemi had 280k I think when totalled,didn't consume a drop of oil,ran like new.
My old 2v had close to 300k when I got tired of it spitting out plugs and pulled it and it still ran great,with around 3000 pounds of nitrous sprayed through it during my ownership.
I've seen many 2v 5.4s go in excess of 300k without issue and the stucco guys on my site have an 03 f150 with 450k,used as a work truck since new,pulling 8000 pounds daily in equipment and materials. The body is best to [censored] but the engine runs great.
In my experience the only way to trash an engine is to run it without oil or coolant,and even poorly maintained vehicles seem to last longer than an owner wants to keep them.