Not that the nose cone would truly look ejectable or anything. What we know canonically about the bow end of the ship is that there is a docking port there, and a navigational deflector beneath, with an orifice capable of firing probes, torpedoes and sometimes phaser beams. To pack all that in a "jettisonable warhead" sounds insanely complicated and counterproductive IMHO.
Even if we take the Tech Manual at face value, we might say that the original warhead function was removed from the bow as useless and unsafe when Sisko acquired the ship in "The Search".
As for the bow being a lifeboat, surely it could hold a crew of 40 in comfort, if not luxury? It's bigger than a runabout, even if we think the ship is just 120 and not 170 m long.
(The original plans for the ship suggested that the "cheek pods" would be the lifeboats, with the bow being the bridge. That was when the ship was envisioned as barely 50 m long, but that's basically why the bow and cheeks look like they do.)
Timo Saloniemi