Can transition on an airfoil occur without prior separation?
can transition occur without the presence of a laminar separation
  bubble?


In short YES.
To elaborate, there are usually 3 mechanisms causing the boundary layer to go turbulent. 


Natural transition  
Forced transition    
Bypass transition


Because the question is about the Natural transition; this is usually caused by sufficiently amplified Tollmien–Schlichting waves. The reason why you see a transition followed by separation in low Reynolds number flow is because in the separated flow, the amplification factor is around 4 times as much as for the attached flow. 


  If yes, what would this look like in a pressure distribution?   





  Here, a clear laminar separation bubble can be seen. The Reynolds
  number has been increased by a factor of 10. The transition point is
  still visible, but it is not so clear anymore whether there is a
  separation bubble. Is there a possible scenario where a laminar
  boundary layer transitions without first separating?


As indicated above, it is possible for a boundary layer flow to make the transition to turbulent without separation. 
N-factor growth rate scales as $\sqrt{RE_\infty}$ for attached laminar flow and for sufficiently enough $RE$ you can easily see the transition undergoing without any separation. 

Also, it's best to inspect the boundary layer parameters through the VPLO menu which gives a clear indication on whether the flow is actually attached or separated.




A very good reference for this is Prof Mark Drela's Flight Vehicle Aerodynamics. - Chapter 4.