If I choose to include failed charges in MRR and then terminate a subscription, will it still contribute to MRR?

If you currently include failed recurring charges in your MRR (Monthly Recurring Revenue) calculation and then terminate the subscription - Yes, that recurring amount will still be included in MRR historically. 

 

If the terminated subscription has an annual billing cycle, the recurring amount for that subscription will continue to be included in the MRR calculation until the billing cycle ends. If the customer later on decides to reactivate the subscription, both the terminated subscription amount and the new subscription amount would contribute to MRR.

For example,

$100 - terminated subscription amount

+ $100 - new subscription amount

= $200 contribution to MRR