Celtic fan here. Been reading this thread a few times the last couple of days so thought I may as well contribute a bit.
I reckon that after the CL qualifiers are over, van Dijk will be off. Regardless of how we got on. You already know but if you do get him, you've got yourselves an absolutely cracking player. He has everything - pace, strength, height, skill, he scores and he can defend. Although in Europe at times, he has switched off. That's the biggest concern, but then again he was fantastic against AC Milan and Ajax. Even played well against Barca.
Hopefully the Nir Bitton suggestion is just that, not an actual rumour. I like Southampton but seeing our two best players go to the same club in the same window is too much!