Bat .. I am sure there are many who are glad he is dead, something which I can understand if they have been bereaved.
However, celebrating his death only gives his supporters more reasons to continue and is a typical example of actions which perpetuate hatred and acts of terrorism. 2 wrongs do not make a right.
If someone feels happy that he has been killed, there is no need for or useful purpose in public celebration.
As Lucy said …. many have lost parents, children, brothers, sisters, friends through war and acts terrorism in all parts of the world – those who we agree with and those we oppose.
By all means have the feelings, but maybe the mature action is to keep them to yourself.