Microwave oven with no heat, Bad design or wrong component choice?
Maybe the connectors were assembled badly or the metallurgy is a bit off. Hard to tell. It's almost surely the female portion which is causing the trouble. Hard to make a tab wrong, but the other bit has the springiness which is essential. It's also possible there is something in your environment (sulfur?) which is corrosive, which could be contributing but there should be enough pressure that is not a problem, especially at mains voltage.  
Nothing beats directly interrupting the power in a permissive chain. Certainly nothing with firmware. Imagine if that relay stuck and all you did was the next best thing and interrupted the coil power- fried corneas or hands - maybe permanent damage. And in any case, your intuition is wrong in this case, lower voltage low current connections are more prone to failing open than those at mains voltage. 
The problem is that the female connectors are loose, nothing to do with the tabs. You can replace the female Faston (quick disconnect) connectors with fresh ones of the correct size and with appropriate approvals and rating- you just lose a bit of wire length. 


The spring action is just the bending of the metal as shown below: 



Cheaper ones will use thin brass, which doesn't make a very good spring, better ones phosphor bronze, and there are also construction differences as you can see in this catalog (which might be a bit overwhelming). 

Be careful and/or get help on this, there are lots of things there that can hurt you, and microwave ovens are stupidly cheap (unless you need one to fit a specific hole, then not so much).