Imagine killing a SPI for an insert statement that was inserting a million rows the time to rollback would be huge. The only time it would be safe to kill a spid would be if its a select and even then its not a good idea and should be more of a last resort after understanding the impact.

Tempdb growing on its own it not an issue if it has freespace in it.

e.g

my tempdb started out at 20 GB and then grew to 100GB

once the transaction committed and the session disconnected all the space allocated (80GB ) is freed up back to SQL ( not the OS). and now SQL can use this space for any new Temp objects being created.

If I ever want that space back i can simply shrink the database.