The sort date is the TMG feature explicitly created to deal with situations like this. Where I have a Death date but no known Burial date, I always use whatever I have entered as a date for the Death, even if it is only approximate. The Burial "Date" will be blank, but I will enter in the Burial "Sort Date" whatever is the Date in the Death tag (e.g. "c Jul 1730") but with a question mark '?' appended (i.e. "c Jul 1730?") which will force the Burial tag to sort after the Death tag.
The Dates section of the "Data Entry" chapter in my book more fully explains the details of using the question mark as a date modifier.
The Sort Date is the essential tool in specifying an order for multiple tags whose Date fields all contain the same date. As examples, see also the Dates section of the "Data Entry" chapter in my book, especially the details of all Sort Date modifiers and their sort order.
You might also check out the "Set Sort Dates" feature in TMG Utility to automatically set meaningful Sort Dates for tags whose Dates and Sort Dates are blank.
Hope this gives you ideas,