How close did Chamberlain come to staying PM

Any thoughts on how many votes in the Commons Chamberlain was hoping for on May 8, 1940 for him to stay in office? I believe about 38 Tories voted against him and 20 or so abstained. At what number would Chamberlain have had second thoughts, or at least decided to try to cling to office for awhile, until events took a different turn, as they did two days later with the German invasion of western Europe.
 
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