You might want to check what layers are on in your layout views (turn them all on and see if your text is still there). I've found it a good idea to have all Master info, including text, on Archicad layer, then you know it is always going to show up. Also remember to change all converted- from- AC9 masters to Archicad layer before merging them in AC10 project, otherwise all Plotmaker layers come in too! (D'oh)
Undo in Layouts is as for modelling, under Options, Work Environment, Data Safety (mine currently set to 20 steps).