Going to the Forest of Shadows to go kill a necromancer within his own home base (which we know is the location of a nexus), to steal his Big Book of Bad Magic... is definitely something we can do.
...I'm actually totally behind the idea, but I'm phrasing it like that to highlight the danger. I think we'd see very decent support from the idea if we use the Gambler (or the Father) while doing so, and maybe bring Johann and/or Egrimm as backup. Mathilde's a lot stronger as a wizard and as a swordswoman than she was when she took down Alkharad's college... But he still very nearly killed her. A certain level of caution is warranted.
And depending on what canon Boney's using, the master of the Tower of Melkhior is separated somewhere between one and three degrees from Nagash. Canon originally is that W'soran got ganked by his apprentice, Melkhior the Ancient, who drained him dry of blood and then ate him. Several thousand years later, Melkhior got ganked by his apprentice, Zacharias the Everliving (though in canon he does that around 2506 IC). One accounting of canon says that W'soran transmitted his spirit to Melkhior, though, so... shrug. Who knows which interpretation Boney is going for.
...Well, regardless of danger to actually assaulting the Tower, the first step is to merely scout it out from a distance, alongside the other Forest of Shadows nexuses. That part we're definitely doing no matter what, I imagine, and I will continue to support the notion of doing so as part of a Father-plan. Haletha is the goddess of Protection from the Forest of Shadows, so who knows - perhaps she'll look kindly upon us and give us a greater narrative benefit than the Gambler's. We'd be acting directly in Her interests, after all.