whip it off, for the time it takes it will be worth it. sort the thread out and you can have a good look at the head.

If needed you can get a skim for around £30

Its quite an easy job, as long as you mark everything and make notes, ive just done a head recon and gasket on a Aston DBS (see resto section), and if i can do that then you should be able to do it

If the tensioner slackened theres a very big chance even tho the belt didnt come of that i has slipped a tooth.

You could always time it up and turn it over buy hand, for the sake of 15 mins, this will give you an indication of how bad the damage is if there is any.

But i wouldnt recomend firing it up, is there is damage to a valve or 2 then you could risk damage to the piston, block and head and then be in a right state.

You will soon see when the head comes off, first signs will be indentations in the piston crown.

If the valves are bent, for £30 you may as well get a skim, and or pressure test for £40
simply replace the valves and lap them in with some paste. check your clearences, head back on, new bolts. jobs a goodun.

good luck mate

can i ask why the tensioner came loose, i presuem you were doing some work, rather than it happening spontaineously (sp) ?