hi
,would have thought the gear selection would still work, just you have no positive neutral position,have you tried refitting the bolt and spring after finding neutral,assuming that this bolt is for the neutral position only,on an xr250 one of the bolts if removed will need a strip down to reset the gear selector
also i would assume they fit into a tube in the casing and as under spring pressure the gear selector mechanism would stop and ball/thing from falling in the gearbox.
pic of the bolt,spring and where it fits may help and location as some one may be round the corner,good luck