While many seem to be of the opinion that Jon shouldn't go meet Dany, I disagree due to several factors...
First, Jon has seen and fought, and killed an Other. Sam is semi-indisposed, he would be a likely envoy to bring that message to Daenerys too, but Jon should go absent Samwell, Edd is busy at CB, but Jon should coordinate with them to send a raven to Dragonstone requesting aid. That would put some pressure on Dany, their would-be ruler to hear their side of things before offering oaths of fealty. Jon will bend the knee because he has no IT ambition, but I suspect he'll have conditions of his own to shed the KitN title, something about Starks always in Winterfell maybe. But Jon needs to fully explain the threat if need be, that'd be a huge knowledge dump to give an envoy and even then some details could be forgotten or omitted, etc. The weight of having your greatest representative go to request aid or an alliance shows desperation sure, but it also speaks to the severity of the situation if he will go despite concern for his personal safety.
Two, Tyrion. If you work through it, Dany is one of if not the only strong ally the North can make. Why would Tyrion who allegedly killed Tywin, Joffrey and thought to have been behind Bran's assassin, ally with Dany when his sister sits the throne? Tyrion knows tensions are exploded between Lannister & Stark, but he has been innocent of wronging Starks, Sansa can verify and has. Tyrion was empathetic to Mormont's plight from his time at the Wall. It has risks, but it also represents one of Jon's best opportunities since Stannis in getting real aid for the NW.
The North and Jon in the same sense need an ally who is strong enough to actually take the throne. Thusfar the IT has ignored/refused all legit requests for aid, Cersei has been behind all of those refusals,, post Robert. What would bending the knee to Cersei change for Jon in that respect? She has wildfyre but not sure if Jon knows this, while Dany has dragons and that he does know.
Of course we need drama among the Northern houses due to LF, but once his arc is reached its zenith, there is little tension in the north reestablishing those strong ties they present from episode 1 of the series.
Don't mind some of the fan service because I suspect some aren't going to be around much longer... Obara and Nym gone so far, plenty more to come!
Seems as though the show is setting up a division of North and East for Dany, South and West for Cersei. Dorne has no leader past Ellaria, seems late to intro a new one now, so I suspect Dorne just won't mobilize, they're done. That leaves the Tyrell split army and the westerlands. The North aren't mobilizing to come south. The Vale army is a wildcard. Dany holds the East.
Makes things neater and gives Euron some purpose outside harrassing Dany's remaining fleet.