Hi Steve and wellcome to the forum
When you see a drum kit you should always keep in mind that for each of the 88 keys of the keybed (-+ octaves included or sometimes drum kits use fewer keys)
a drum kit is using each key for a specific drum sound.
Let's say I make a drum kit which I call it Heavy Metal kit and in the note B3 I have a snare drum sound,on the note A6 I have a bass drum sound etc.
When a style is playing,it can read those notes to produce the sounds of the drum.
(Every sound of the style parts is written as notes).
If I delete this drum kit from my keyboard,as Joe said, the style will choose another drum kit to play and on that drum kit the note A6 is no longer a bass drum sound but a cymbal sound and the style now may sound really funny.
Same thing will happen with the other sounds.
e.g a deleted violin from from an expansion pack.
So you have to know which styles are using those drum kits and if you use them or not as Chris said because drum kits are crucial elements of a style.
Of course everything can be replaceable in a style and you can copy the drum parts from one style to another,make some changes to existing drum style parts or even create a new drum part.