As, used in the Octavia in the Superb, as I am thinking of buying one but it would be a high miler, and would like to know there would be an engine that will drop in if the high miler goes wrong

Almost any VAG petrol/diesel engine. The 1.9Tdi PD 105 (non-DPF) is a pretty bulletproof engine, unlike the 2.0Tdi PD140.

My remapped 1.9Tdi Superb II clocked up 95,000 miles in 33 months with no issues whatsoever. The average 57mpg (brim to brim method) was also highly commendable.