When it's a paid project, so it's best to be transparent, I'm sure people would like an update on how this is game is progressing, how you're doing and wish you well regardless of whether you're able or unable to complete the project, myself included
But is this expansion pack and the major base game update still a thing?
If not, refunds are best, it's not fair for buyers to give money and then the creators go radio silent, aside from a kickstarter post for a different game that had an update, on people who paid for this content for over a year now