Troy only missed race two at Doni after crashing in race 1 (2007). He was back on the bike in Valencia about two weeks later. The missing finger didn't seem to cause any problems but the "other" injuries did. There were stories of trying to find him a cricket box to wear to protect the damaged area but as they don't play cricket in Spain they had no luck and he had to brake rather carefully and make sure the bike didn't tank slap!
Didn't do too much to trouble the scorers that week but came back strong at Assen beating JT to the honours in Race 2 by .009s. See
http://www.youtube.com/watch?v=bds9X7GBxeQ