Like many people here, I would really like WP and YSL to come clean and tell us the truth. However I also think that from WP's point of view, remaining silent may be the best strategic thing to do, after doing their maths and calculations.
It's still early into the term, being 4 more years before the next GE. There's still a lot of time to wait and see what develops, then react accordingly. Making an early hasty decision now that they may regret later is likely to be a bad idea. What has happened is going to lose them some votes, but will it be a significant amount of votes? If YSL stays at Hougang SMC, is he going to lose the 30% margin he held? Is WP going to lose the 8% margin they held in Aljunied? It's possible, but really highly unlikely.
If LTK had big plans for YSL's future with WP, then they will probably have to be shelved, possibly for good. WP's immediate goal is to keep Hougang and Aljunied safe while trying to make headway into other constituencies. YSL can still play an important part in this by staying behind in Hougang to keep it safe. Dumping YSL and replacing him with someone else is not only unlikely to affect the polling results, but a waste of a good candidate being moved from another constituency into Hougang.
Seriously, expecting WP or any politician to be a pillar of morality is being simply naive. Their primary goal is to win your votes, and to do that they just need to make sure you like them more than the other guy. How many people are going to say "I hate the PAP. WP is becoming like the PAP so I hate WP. Therefore I am going to vote for PAP instead of WP."?