From the moment of her own accession in 1558 to her literal deathbed in 1603, there was a great deal of uncertainty as to who would be HER successor (and from a purely logical point of view, it's rather astonishing that James VI was able to succeed smoothly at all). However; before the Queen of Scots' Execution, there was little if anything to keep England from devolving into chaos upon Good Queen Bess's passing.
Could there have been an all-out Civil War between Protestants and Catholics each trying to champion their closest heir or could Parliament have attempted to abolish the monarchy upon the last Tudor's death? Any ideas?