Sql Server Transaction logs during large deletes
We don't know why your transaction log backups will fail but we can discuss solutions. He could be concerned about transaction log bloat, when the transaction log would grow so large that it filled the drive where the log file is stored.

First, and easiest solution: If you're moving all the data out of the table entirely, simply truncate the table. This is minimally logged.

Second: Split your DELETE statement into batches. Find a way to divide your data, let's say in batch sizes of 5,000.

DELETE FROM OldDBTable
WHERE ID IN 
          (SELECT TOP 5000 ID 
           FROM OldDBTable 
           WHERE [Statement to define deleted data here])


You could probably increase that batch size if you want. Then just set a 
WAITFOR DELAY '0:05:00' to wait 5 minutes for your next batch.