I'm pretty sure Stripe will NOT send a declined email if you've turned off email receipts in stripe (under Business Settings in Stripe)
If you have turned them off, you'll need to rely on your EOT reminder emails to do the job for you. e.g. have a email(s) timed in line with Stripe's attempts to take payment again (under Subscriptions->Settings in stripe)
Importantly, you'll need to have followed the instructions here to make sure EOT emails work for recurring payments, and there's a couple of watch outs listed on that page as well, so this approach may not work for everyone.