Don’t know if this is working, but might be worth a shot. Someone posted this on Google Docs help forum.
/.../ If you want more than 50,000 characters in a single cell, you can use QUERY's header clause.
Example:
=ArrayFormula(query(row(A1:A70000),,100000))
This creates a cell with 408,893 characters. You can verify by using the LEN function.
Ok I fixed the above line like this, I think it works:
=ArrayFormula(query(A1:A100000,,100000))
This is provided that you have data in column A, from row 1 to row 100000. It will concatenate all of it. I guess max length is 100000 characters?