I'd agree that *animation* is isometric games certainly involves more work, because you'll have to render frames for each facing direction, but that's nothing to do with pathfinding!
If you want to disallow diagonal paths in the route returned by the pathfinding plugin then you need to delete/comment out the diagonal cells added to the openlist in lls 380 and 402 of pathfind.js, so that you only have the following:
if (!obsLeft)
this.addCellToOpenList(x - 1, y, 10);
if (!obsTop)
this.addCellToOpenList(x, y - 1, 10);
if (!obsRight)
this.addCellToOpenList(x + 1, y, 10);
if (!obsBottom)
this.addCellToOpenList(x, y + 1, 10);
// Diagonal cells commented out as follows
//if (!obsLeft && !obsTop)
// this.addCellToOpenList(x - 1, y - 1, 14);
//if (!obsTop && !obsRight)
// this.addCellToOpenList(x + 1, y - 1, 14);
//if (!obsRight && !obsBottom)
// this.addCellToOpenList(x + 1, y + 1, 14);
//if (!obsBottom && !obsLeft)
// this.addCellToOpenList(x - 1, y + 1, 14);
Don't know how that fits with the general policy of "not editing the core plugins" though...!