If you really want this to work you need to invest your players in a place, build their confidence, advance the plot and then introduce the BBEG.
1) Invest the players in a place or a task, so that they won't run away. How about having your new home town besieged after the PCs enter? Once the city is surrounded, they are in the adventure. I know some people will say this is heavy handed but your group sounds lacking in confidence. They need to achieve something and see it through to gain confidence, and sometimes this takes a little push from the DM. Are they new to gaming?
2) Build confidence; Once in the city, as the siege is going on, the PCs become important because gradually most of the other high-level important figures in the town negotiate their way out, including the BBEG (much to the ire of the common people) or die in the conflict. The Siege need not directly involve the PCs too much but have a few encounters where they are given a task that can endear them to the local populace e.g. protecting food and water or raiding the enemy camps, holding a church full of common people, discovering food hoards of corrupt nobles and giving it away, fighting a massive fire that threatens the whole town etc. Once they have done something noteworthy, have news of this spread through the town and have the common people show them deference in a few encounters.
Then have the PCs involved in some simple encounter, perhaps they take care of someone ill or save someone from looters etc. The person they help eventually dies but leaves them a building of some kind as a thanks. The building is a business, has a safe place where the PCs can stay and generates them a modst amount of money. It also has a competent person running it. Thus the PCs become invested in the town, gain a base and so a reason to stay and protect their holding, feel good about themselves and gain some structure to their existence.
After the siege, the person expecting to inherit (BBEG) arrives and is a powerful individual in the town. They fled during the siege and so all the commoners hate this BBEG because they left them to die.
Now the BBEG wants to get rid of the PCs to claim the inheritance that they think is rightfully theirs but cannot act because their own position is so precarious because of the way they carpet-bagged the town during the siege. The PCs now have the general friendship of the townspeople and a little bit with some of the noblest nobles who stayed behind but the dire hatred of this BBEG noble/magistrate/etc.
The PCs can try to kill the BBEG if they like but if you make them so temporally powerful that it is currently impossible (surrounded by bodyguards, food tasters, finest locks and haevily guarded houses and estates). Now you have a balance of power. Have your adventures maintain this balance for a while and it will become entrenched and the theme of the campaign.
Hope this helps; just one example of how to do things.
