Row ordering after CREATE TABLE AS...SELECT regexp_split_to_table(source_text, regexp) AS new_column

This is a two-part question:

1) I have a source_text that I want to divide into smaller subunits
that will be contained in rows in a column in a new table. Is it
absolutely certain that the initial order of the rows in the resultant
table after this operation:

CREATE TABLE new_table AS SELECT regexp_split_to_table(source_text,
E'regexp') as subunits FROM source_table;

will be the same as the order of these subunits in the original text?
Emphasis *initial order*.

2) I would like to be able to create a serial-type column during
CREATE TABLE AS in the new table that "memorizes" this order so that I
can reconstruct the original text using ORDER BY on that serial
column. However, I am stumped how to do that. I do not see how to
put the name of that column into my SELECT statement which generates
the table, and I do not see where else to put it. Please forgive my
stupidity.

The "work-around" to this problem has been to ALTER my table after its
creation with a new serial-type column. But this assumes that the
answer to Question 1) above is always "Yes".

Thanking you for your understanding,

John