Lucius threw Dumbledore out of Hogwarts by Tom's diary. A basilisk is let out, wandering in the school and hunting students. What is his original plan to handle this? Fighting a basilisk by himself?
The Basilisk was only reported to kill mudbloods and the likes, so not children Lucius would be concerned about.
I think his plan was two, maybe threefold:
- Use the book to unleash the monster, killing mudbloods and closing the school.
- Discredit Arthur Weasley and get him fired/imprisoned.
?3. Reopen school with him at the head?
I think he just planned to ignore the monster or hoped it would go back to sleep for years.
Lucius didn't want to fight the Basilisk. Remember- He was the one who put the diary there in the first place in order to open the Chamber of secrets.
I understand that Voldemort had told him the diary would cause the Chamber of Secrets to reopen because it was cleverly enchanted.
Lucius planted the diary in Hogwarts for a few reasons:
To open the chamber and kill all the muggle-borns.
To get Arthur Weasley in trouble.
Get Dumbledore out of the school.
To get rid of a dark artifact because Arthur Weasley was conducting raids
"You have heard, of course, that the Ministry is conducting more raids," said Mr. Malfoy,
"I have a few - ah - items at home that might embarrass me, if the Ministry were to call..."
I think it was mostly to get rid of his political opponents, I don't think he planed on fighting the basilisk, I suspect he didn't even knew what it was.
I think he planed on having Dumbledore sacked (success) and having the school closed so when that happened he could somehow have Ginny searched either on the train back home or while at the burrow so he could frame Arthur.
Remember we don't see things from the perspective of anyone other than Harry so the apparent disappearance of Ginny might have come as a surprise to him, specially since Voldemort never told him what the diary was and I don't think he is so stupid so as to tinker with it.