Delta table update if column exists otherwise add as a new column

I have a delta table as shown below. There is a id column and columns for count of signals. There will be around 300 signals and so the number of columns will be approx 601 in the final delta table.

The requirement is to have a single record for each id_no in the final table.

+-----+--------------+-----------------+--------------+-----------------+--------------+-----------------+--------------------+..............+------------------+--------------------+----------------------------+
|id_no|sig01_total   |sig01_valid_total|sig02_total   |sig02_valid_total|sig03_total   |sig03_valid_total|sig03_total_valid   |..............|sig300_valid_total|sig300_total_valid  |load_timestamp              |
+-----+--------------+-----------------+--------------+-----------------+--------------+-----------------+--------------------+..............|------------------+--------------------+----------------------------+
|050  |25            |23               |45            |43               |66            |60               |55                  |..............|60                |55                  |2021-08-10T16:58:30.054+0000|
|051  |78            |70               |15            |14               |10            |10               |9                   |..............|10                |9                   |2021-08-10T16:58:30.054+0000|
|052  |88            |88               |75            |73               |16            |13               |13                  |..............|13                |13                  |2021-08-10T16:58:30.054+0000|
+-----+--------------+-----------------+--------------+-----------------+--------------+-----------------+--------------------+..............+------------------+--------------------+----------------------------+

I could perform the upsert based on the id_no using delta merge option as shown below.

targetDeltaTable.alias("t")
  .merge(
    sourceDataFrame.alias("s"),
    "t.id_no = s.id_no")
  .whenMatched().updateAll()
  .whenNotMatched().insertAll()
  .execute()

This code will execute weekly and the final tabe has to be updated weekly. Not all signals might be available for every week data.

But the issue with merging is, If the id_no is available, then i have to do an additional check for the columns (signal columns) availability also in the existing table.

1. If the signal column exists then i have to do an addition of the new count with existing count.

2. If the signal column does not exists for that particular id_no then i have to add that signal as a new column to the existing row.

I have tried to execute delta table upsert command as shown below, but since the number of columns are not static every data load and considering the huge number of columns it was not succeeded.

DeltaTable.forPath(spark, "/data/events/target/")
  .as("t")
  .merge(
    updatesDF.as("s"),
    "t.id_no = s.id_no"
  .whenMatched
  .updateExpr(//some condition to be applied to check whether column exists or not?
    Map("sig01_total" -> "t.sig01_total"+"s.sig01_total"
                      -> 
                      ->........))
  .whenNotMatched
  .insertAll()
  .execute()

How can I acheive this requirement? Any leads appreciated!