We can expect that Conor Lamb, who is more likely than not going to be declared the winner, will wobble on guns and is not as pro-second amendment as he claims. But it must be notable that Lamb ran as a gun owning, gun rights supporting Democrat. He fit his district, which is what the Democrats are trying to do despite progressive activists' complaining.
Given the vast array of seats up for grabs this year, it will be very hard for Democrats to use the gun agenda as anything other than a way to rally their progressive donors, who will then get very little in return. They may be able to raise the rifle purchase age to 21. They might ban bump stocks. But there is already some bipartisan support for the former and a lot for the latter.
They will not, however, be able to return to "assault" weapons bans, etc. It will be difficult for them. That will enrage the progressive base. But as Democrats pick candidates who look like their districts, it is going to be hard to get highly progressive candidates through the front doors of Congress except in urban areas Democrats already hold.