Migrating data from multiple spreadsheets to multiple text files
This looks quite clean in general. May I suggest a few minor improvements:


I think you could just use workbook.active to get the sheet
instead of doing the rstrip(".xlsx") which would also right-strip out .sslsx or sl.xs.ss and even grab a part of the actual filename:

In [1]: "christmas.xlsx".rstrip(".xlsx")
Out[1]: 'christma'


use os module or the beautiful pathlib to properly extract a filename without an extension:

In [1]: from pathlib import Path

In [2]: Path("christmas.xlsx").resolve().stem
Out[2]: 'christmas'

calculate what you can before the loop instead of inside it. For instance, sheet.max_row is something you could just remember in a variable at the top of your function and re-use inside. It's not a lot of savings, but attribute access still has its cost in Python:

max_row = sheet.max_row

something similar is happening when you get the value of a cell twice, instead:

cell_value = sheet.cell(column=column, row=row).value

if cell_value:
    textfile.writelines(cell_value + '\n')

it may be a good idea to keep the nestedness at a minimum ("Flat is better than nested.") and would rather check for a reverse condition and use continue to move to the next iteration:

for column in range(1, sheet.max_column + 1):
    if not sheet.cell(row=1, column=column).value:
        continue

    text_filename = get_text_filename(filename, column)



Some out-of-the-box ideas:


feels like if you do it with pandas.read_excel() it may just become way more easier and beautiful