Should the Sarah Jane Adventures continue?

[chardman]

and with Doctor Who, there's a built-in construct to replace the actor after a given time.

There is now. But it certainly wasn't a planned aspect of the character from the get go. They didn't come up with the device until Hartnell wanted out.

Sarah Jane is a human being, and not only is she the lead, she's the show's namesake.

And the very same things were originally true of Hartnell's Doctor, until the writers decided to change him into an alien to better accommodate the kind stories they wanted to tell, and so that they could explain the non-human notion of regeneration so that the show could later continue with a new actor in the same role.

Now, this is all moot, as CBBC has announced that this will be the few episodes already filmed will appear as the very last series of "The Sarah Jane Adventures".

Or is it?

I wouldn't be surprised if before this 6th series is over, the CBBC announce a replacement series that utilizes some of the surviving characters from SJA, and is virtually identical to SJA in just about every way except with a different lead character and a series name that reflects this change. It'll be just like when "Life on Mars" ended prematurely, and "Ashes to Ashes" took it's place. Same basic cast with a few changes, same basic plot with a few changes, same basic show with a new title.