At point 1: The TO how? Sleep in the train?
There always a Plan B (Modified from your query)
Example: The last train for EB from in Joo Koon is 10pm
So, assuming from Clementi - Joo Koon takes 15 minutes
Then, the train may park there for 5 minutes
In total it means by 9:40pm, the last EB train from Joo Koon
should be in Clementi ready to depart and head towards Jurong
East.
And thus any train after 9:40pm in Clementi will be a DNB,
either do a turnaround for EB in approaching UPD or directly sleep
in UPD
But, the problem is Clementi is a crowded station, so does Boon
Lay. It effectively suggest the last train from Pasir Ris to Joo
Koon is about 8:30pm to 9pm, which kind of difficult.
But there is a Plan C.
Any train after 9:40pm will have a special train bridging
service from Clementi - Lakeside and Lakeside - Joo Koon.
We will first talk about Lakeside - Joo Koon, since it is
easier.
For this, both platform will presume as normal, since Lakeside
got a Tandem crossover (Same as Boon Lay, except Boon Lay's is
before the station and Lakeside is after it, in terms of WB).
Special staff logistic is needed in Lakeside to tell passengers the
train is heading either Clementi or Joo Koon.
Since there are 4 stations, I presume they can deploy 4 to 6 for
it (Joo Koon's distance is quite long).
Then the Clementi - Lakeside is more tricky.
Due to lack of crossover before Lakeside (In terms of WB), most
likely they will provide a bus bridging service OR provide only 1
train from Clementi - Lakeside (But the frequency will be like
every half an hour per train). Since the entire route has no
crossover for Lakeside - Clementi, so it is really not possible to
do much.