Oh man, I just found out about this sad news. The following news statement is taken from the site of U2U, the company that he cofounded:
It is with deepest regret that we have to announce the death of Patrick Tisseghem, co-founder of U2U. Patrick suddenly passed away on Wednesday 3 September 2008 around 18 hours in Gothenburg Sweden due to a heart failure. Our sympathy and thoughts go out to his wife Linda, their daughters Anahi and Laura, and to his family. We are all deeply saddened by this tragic loss. We remember him as caring father as well as a driven and warm hearted colleague and friend. We miss you Patrick.
I followed one of his courses about Sharepoint several years ago and especially requested for a course given by him because I knew he was a world known expert on that particular topic. After that we met occasionally and moslty saw each other thanks to Microsoft related conventions or like a couple of months ago when we had a meet and greet with Tim Sneath.
I'm the guy on the left, then Peter and then Patrick himself. This is truly very, very sad news for his family as well for the community.