Erm, yes it can - the cam follower slides can be inspected through the push rod tubes with a torch - if the full hemispherical push rod seat is present, the slide is OK. The Tappets are ont he rocker arms, so they can be inspected just by removing the rocker cover.
Frankly, if the follower slides are OK, and just the push roads are bent, there is absolutely no reason to remove the head. As I said, the valves and pistons share the same axis (vertical), so they don't impart any lateral force on each other if they make contact, and it's lateral forces that would cause bent valves. You'll probably have a very shallow valve imprint on the piston heads that contacted any valves, but they won't have any effect on the engine. Most engines have inclined valves which are offset from the piston axis, and contact in such engines creates significant damage to both pistons and valves, but the 4-cylinder 2.25 and 2.5 engines (incl Tdis) and the TD5 benefit hugely from this more robust configuration (I don't know what the Tdci is like inside, or the V8s, V6s and so on).
Following an inspection of the valve operating gear, fire it up and you'll soon hear if there are any problems. DOing this won't create further issues if a bad test run is kept short.
