Change in Index costing because of blevel change

We are having a situation in which multiple queries suddenly changed the execution path and deviated from the local indexed access path to the FTS path(partition range all) for a daily range partitioned table. And then after debugging into the issue we found that the COST of the index access actually has been increased because of the increase in BLEVEL of the index. And the BLEVEL has been increased from 2 to 3 in global level(dba_indexes) because of one of the missing daily partitions. For e.g. 14th jun partition was missing , so 15th jun partition now holds both 14th june and 15th jun data, so its twice as bigger as a normal daily partition.

The missing day range partition caused the subsequent day partitions to actually hold two partitions/days worth of data and thus the blevel of that specific local index increased from 2 to -3 for that index partition. and since then, in global level(dba_indexes) the blevel is staying as-3 for that index, costing that index access higher and thus making plan change for many queries.

My question is how should we handle such a situation ? Should we go back and break the specific partition(15th Jun partition) into two daily range partitions i.e. 14th and 15th (which i believe is going to take lot of time and resources considering this table has ~8 different local indexes in it) and gather stats again or is there any other way to just tweak the stats for that one big partition such that the global index BLEVEl can be back to
-2 , and get this issue fixed?