I think that the key information here is "with Ledger" part. I think that split or no split, if you are using Ledger you are good and safe - you are the owner of your keys and even if MEW for whatever split-related reason ceases to exist anymore, you will be able to access your founds in another client.

And using Ledger additionally safeguards the key from third parties, even if the split-related party changes the MEW site code so it is compromised.