There is a level of functioning of the network this is not a problem. The bigger question is if you have any internal services that you need to publish to the internet (Like a web server).
Ideally, each MX would have a public IP, but if that's not possible, that's fine, that's one of the advantages of using SD-WAN, you don't depend on a dedicated link.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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