If May goes now she should resign only as prime minister and remain leader of the Tory party until the Brexit programme is decided and implemented. She can then resign as Tory leader in time for an election by party members to conclude at the party conference in the autumn.
A caretaker PM should be appointed now by the Queen, backed by the cabinet, to lead the Brexit process until either:
a A Withdrawal Deal is passed and put into effect
b A long delay involving EU elections is decided on
c Brexit is cancelled
d The Tory led government falls.
Meanwhile the House of Commons remains divided and in turmoil. It is not clear that anything can be agreed on unless a more scientific voting system is adopted to establish preferences, leading by elimination to a choice. These votes must be unwhipped and free. Otherwise we are, through accident and paralysis, headed for a crash out on April 12th.