There's a high chance of getting banned with the MIG Switch if you're using publicly available dumps or mixed dumps (e.g. XCI and Initial data files from the Internet and the rest of the cert files from a donor cart that you've bought new and dumped). However, if you're using a full dumps of the carts you own and you're 100% sure they weren't dumped in the past and are publicly available, there shouldn't be a problem.
Based on what I've gathered in this thread, it's fine if you form a group with some other people that own multiple cartridges and share your cartridges between each other as long as you make sure that two or more are playing the same game at the same time (not sure if you can play the same game at the same time offline, though, as I'm not sure what's logged on the consoles). This is probably the only way other than dumping your own cartridges to stay safe and avoid getting banned. At least, for now, unless Nintendo decides to push a firmware update with MIG Switch (and alike) detection in place, provided that's possible.
Note that, even if you get banned, you can still update the firmware on your console the official way. eShop and online stuff is out of the question. As for the updates, there's a workaround with updating games by matching the version of the game on another console via local network. DLCs are, unfortunately, only available if they are already available in cartridges you own or have dumps of on your MIG Switch.
I hope that answers your question. If you aren't using online services at all, even if you get banned you aren't missing out much.
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