Plenty of bats have gone from above 50 to below 50 at the tail end of their careers recently. Sehwag, Clark, Jayawardene, G Smith spring to mind.
Inzamam-ul-Haq, Misbah-ul-Haq, JC Adams, Saeed Ahmed, Sarfraz Ahmed, DL Amiss, HM Amla, M Azharuddin, GS Ballance, EJ Barlow, KC Bland, BC Booth, G Boycott, DM Bravo, WA Brown, BF Butcher, SL Campbell, MJ Clarke, HL Collins, AN Cook, RM Cowper, Q de Kock, ER Dexter, BL D'Oliveira, PJL Dujon, F du Plessis, GA Faulkner, JHW Fingleton, G Gambhir, SC Ganguly, AC Gilchrist, DI Gower, CG Greenidge, AW Greig, Mominul Haque, J Hardstaff jnr, RN Harvey, AL Hassett, VS Hazare, EH Hendren, DPMD Jayawardene, AH Jones, DM Jones, AI Kallicharran, Mohsin Khan, UT Khawaja, WM Lawry, DS Lehmann, DR Martyn, AD Mathews, SJ McCabe, RB McCosker, CC McDonald, CP Mead, Shoaib Mohammad, AR Morris, NCL O'Neill, PH Parfitt, KP Pietersen, WH Ponsford, G Pullar, AM Rahane, JF Reid, MH Richardson, LG Rowe, JA Rudolph, JD Ryder, TT Samaraweera, V Sehwag, MJ Slater, GC Smith, RA Smith, JB Stollmeyer, AJ Strauss, MA Taylor, IJL Trott, GM Turner, MP Vaughan, KD Walters, DA Warner, WM Woodfull and FMM Worrell all averaged over 50 at one point (having scored at least 1000 runs).